Calamos Investment Trust N-CSRSCertified semi-annual shareholder report (management investment company)

The 33.79% S&P 500 Index decline from February 20 to March 23 delivered a stiff headwind to the hedged equity portion of the Fund. The Fund benefited from the put and short call options in place, but the equity basket fell below the call and put option. The Fund also benefited from the active management of our option trading, given we were able to take profits in the calls after the market decline while maintaining the existing put positioning. This meant that we were able to “clear the runway” so that we could participate in more of the market rebound (from March 24 forward) than we gave up during the pullback.

The convertible arbitrage portion of the portfolio fared better than the hedged equity strategy during the significant market decline. The strategy benefitted from increasing volatility, though this benefit was offset somewhat by widening credit spreads. According to Bloomberg Barclays, high yield credit spreads widened from 415 basis points to 766 basis points during the six months ended April 30, 2020.

Elevated option skew¹ flattened during the reporting period. The Credit Suisse “Fear Barometer” Index, an index that compares the relative value of calls versus puts and is useful for measuring option skew, had begun the period at 25.24 and ended at 23.33 above its historical long-term average of about 20, though it did decline to 14.38 on March 12. As option skew flattened, the Fund’s “North Star” trade, which entails selling 80% calls against 40% puts, became increasingly attractive. Steeper skew provided an affordable opportunity for the Fund to use call and put spreads to create a favorable risk/reward profile.

In response to theCOVID-19 crisis, the Federal Reserve reduced interest rates to near zero and initiated further quantitative easing activities. These actions moved U.S. interest rates sharply lower across the yield curve. The3-year U.S. Treasury yield declined from 1.52% to 0.24%, the5-year Treasury yield dropped from 2.98% to 0.36%, and the10-year Treasury yield declined from 1.69% to 0.64%. While the Fund won’t have significant interest-rate exposure, this generally also means that it won’t have interest-rate opportunity. Declining interest rates over the reporting period supported the Bloomberg Barclay’s Government Credit Index outperformance relative to the Fund. Still, the Fund held up well relative to equities during the reporting period and helped add stability to the equity portfolio.

How is the fund positioned?

At the end of the reporting period, the Fund had 55.7% in convertible arbitrage and 43.4% in covered call writing. The relatively heavy allocation to convertible arbitrage reflects the opportunity we had to invest in robust new convertible issuance that offered favorable terms and valuations. Per ICE BofA, the U.S. has seen $26.4 billion in new issuance so far in 2020 through April 30. Annualized, this would put 2020 U.S. issuance on track to exceed $79.2 billion and would be the highest annual issuance witnessed since 2007.

During the significant market pullback, we took profits from our call positioning and worked to clear a runway to provide upside as the market recovered, all the while maintaining a significant amount of puts to help reduce market participation

CALAMOS HEDGED EQUITY FUND

INVESTMENT TEAM DISCUSSION

Please discuss the Fund’s strategy and role within an asset allocation.

Calamos Hedged Equity Fund is designed to dampen volatility within an equity allocation.

How has the Fund performed?

For thesix-month period ended April 30, 2020, Calamos Hedged Equity Fund returned-0.04% (Class I shares at net asset value) versus the S&P 500 Index decrease of-3.16% and the Bloomberg Barclays U.S. Aggregate Bond Index 4.86% increase. Since its inception on December 31, 2014, the Fund gained 4.90% on an annualized basis (Class I shares at net asset value) versus 8.92% for the S&P 500 Index and 3.80% for the Bloomberg Barclays U.S. Aggregate Bond Index.

In this strategy, we utilize covered call writing, puts, as well as put and call spreads for income and risk mitigation on our proprietary basket of equities that represents the broad stock market. Through active management, we are attempting to derive better risk-adjusted returns versus holding the index passively.

What factors influenced performance?

The markets started 2020 with a steady upside tilt. The upside momentum stalled on February 19 when it began to sink in that theCOVID-19 crisis was much more than a regional Chinese problem. To add to the drama, a rift between OPEC and Russia precipitated a slide in oil prices that had the WTI trading in negative territory for the first time in the history of the contract. Stunned investors looked on as three-years of S&P 500 Index gains vaporized in a matter of days. All told, the S&P 500 saw a 34% decline in March period followed by a roughly 15% bounce back beginning in late March through the end of April. Calamos Hedged Equity Fund road this unprecedented move, limiting downside capture to 35% and the rebound almost instantaneously brought the Fund to breakeven by April on a year-over-year basis. This environment provided favorable opportunities to monetize volatility, as we rebalanced our option hedges, improved the risk/reward positioning, and locked in profits.

The S&P 500 Volatility Index (VIX) increased from 13.65 (01/02/2020) at the beginning of the period to 85.47 (03/18/2020) at a pace and levels that have never been seen,

Our perception proved correct, as Q1 devolved into the worst quarter for equities since 1987, characterized by the sharpest bear market in recent history. After a rather benign first half of the quarter, equity markets rushed to discount the impact of the government mandated shutdowns across many sectors of the economy.

Although the Q1 correction was driven by investors’ reaction to the magnitude of virus-induced economic damage and the unprecedented oil price collapse, the year began with a dubious combination of above-average equity valuations coupled with below-average earnings growth in an economy that was exhibiting late-cycle characteristics.

Since its inception on May 1, 2002, the Fund has returned 9.71% on an annualized basis (Class I shares at net asset value) and, therefore, markedly outperformed both the MSCI World and S&P 500 Indexes, which returned 6.86% and 7.80%, respectively during that time.

What helped and hurt performance over thesix-month period?

The largest contributors were from long investments in the health care and communication services sectors, while long positions in financials and industrials hindered performance. Notable contributors during the period included short positions in the S&P 500 Index Fund (SPY), which serves as a general market hedge, as well as long positions in United Healthcare Group 2.1%* (Health Care) and Tesla 0.7%^† (Consumer Discretionary). Detractors included long positions in Boeing Company 1.9%* (Industrials) and Royal Bank of Scotland 2.8%* (Financials) and Royal Dutch Shell 2.7%* (Energy).

How is the Fund positioned in the context of the global economic cycle?

Investors are grappling with unprecedented uncertainty and little guidance or analogies from the past. How well one manages through this chaos often comes down to one’s psychological bias.

The bull case for equities is straightforward. Unprecedented monetary and fiscal policies will stabilize the system; valuations are now sensible; and Americans will embrace effective healthcare policies. The virus is not the crisis: rather the crisis is the poor preparation of the U.S. government and healthcare system, which can be fixed. The bear case is the flipside of these issues, with an ominous possibility that the virus is not contained and could return with a vengeance later in the year.

We are watching a cyclonic battle between the disease, its economic ramifications and extraordinary policy responses. Skilled labor was a scarce resource just a few months ago, and policy actions aim to keep labor and businesses connected. We think policy will win out. When economic activity resumes, we believe markets will enjoy a sharp rebound. In our opinion, we shouldn’t see the S&P 500 Index below 2400 by autumn.

Since October 2018, we have viewed the equity world through the lens of transition. The investment regime of the post-2008 period gradually gave way to a new era, one whose contours were not immediately visible, and the risk versus reward for equity investors did not add up.

AVERAGE ANNUAL TOTAL RETURN^† AS OF 4/30/20

Performance data quoted represents past performance, which is no guarantee of future results. Current performance may be lower or higher than the performance quoted. The principal value and investment return of an investment will fluctuate so that your shares, when redeemed, may be worth more or less than their original cost.

As of the prospectus dated 2/28/20, the Fund’s gross expense ratio for Class A shares is 3.00%, Class C shares is 3.74% and Class I shares is 2.73%. The expense ratios shown above may differ from the more recent expense ratios reported in the Financial Highlights section of this report.

NOTES:

The graph does not reflect the income taxes that you would pay on fund distributions or the redemption of fund shares. Fund performance includes reinvestment of dividends and adjustment for the maximum sales charge for Class A shares. The performance of other classes will vary from the performance of the class shown based on the difference in sales charges and fees paid by shareholders investing in different share classes.

The S&P 500 Index is an unmanaged index generally considered representative of the U.S. stock market. Source: Lipper, Inc.

The MSCI World Index (U.S. Dollars) is a market-capitalization weighted index composed of companies representative of

the market structure of developed market countries in North America, Europe and the Asia/Pacific region.

Index returns assume reinvestment of dividends and do not reflect deduction of fees and expenses. It is not possible to invest directly in an index.

attributes. The market pullback also created an opportunity to revisit several holdings that we had previously sold or trimmed when they had become overly equity sensitive. In addition, the wider credit spreads and increased volatility seen late in the reporting period spurred an increase in new convertible issuance and provided attractive opportunities on a selective basis.

In terms of economic sectors, the Fund’s largest portfolio weights reside in information technology and consumer discretionary on an absolute basis. Conversely, energy and consumer staples represent the smallest absolute sector weights. On a relative basis, the largest industry overweight positions are systems software and internet services & infrastructure. Relative to the ICE BofA All U.S. Convertibles Index, the Fund holds underweight allocations to financials and health care, with mortgage REITs (financials) and pharmaceuticals (health care) among the underweight industries.

Allocations to consumer discretionary and industrials rose during the period with increased weights in internet & direct marketing retail and airlines. By contrast, allocations to financials and information technology decreased over the period, with reductions to diversified banks and semiconductors.

What are your closing thoughts for Fund shareholders?

Our belief has always been that the flipside of volatility is opportunity and the recent drawdown of the market has provided significant opportunities going forward in our view. Convertible new issuance has increased significantly, as many issuers have sought capital to withstand the near-term impacts ofCOVID-10. Wider credit spreads have made traditional financing more expensive for issuers, and increased volatility has meant that issuers see an increased benefit with including an option in their debt. Many of these issuers have a short-term cash issue but present long-term opportunity. The convertible structure allows investors to participate in the recovery, while providing a measure of downside mitigation should conditions worsen before they improve. This said, we view active management to be essential in approaching the convertibles market. Not every new issue presents an attractive investment opportunity, so having a seasoned management team with a rigorous investment process is important.

Looking forward, we expect convertibles to benefit from narrowing credit spreads, normalizing equity prices, and richening convertible structural valuations. The convertible market also has a relatively heavy representation in the growth areas of the market that we view as attractive—particularly in the technology and health care sectors. We expect uncertainty to remain in the market, given the cloudy long-term impact ofCOVID-19 and a contentious U.S. presidential election. We believe that our focus on continually seeking to improve the overall/risk-reward of the portfolio will serve investors well during the potentially challenging and volatile time ahead.

AVERAGE ANNUAL TOTAL RETURN^† AS OF 4/30/20

Performance data quoted represents past performance, which is no guarantee of future results. Current performance may be lower or higher than the performance quoted. The principal value and investment return of an investment will fluctuate so that your shares, when redeemed, may be worth more or less than their original cost.

As of the prospectus dated 2/28/20, the Fund’s gross expense ratio for Class A shares is 1.17%; Class C shares is 1.92% and Class I shares is 0.92%. The expense ratios shown above may differ from the more recent expense ratios reported in the Financial Highlights section of this report.

NOTES:

The graphs do not reflect the income of taxes that you would pay on fund distributions or the redemption of fund shares. Fund performance includes reinvestment of dividends and adjustment for the maximum sales charge for Class A shares. The performance of other classes will vary from the performance of the class shown based on the difference in sales charges and fees paid by shareholders investing in different share classes.

The ICE BofAML All U.S. Convertibles Index is comprised of approximately 700 issues of only convertible bonds and preferreds of all qualities. Since inception data for the index is shown from 6/30/97, since data is only available for full monthly periods. Source: Lipper, Inc.

The S&P 500 Index is an unmanaged index generally considered representative of the U.S. stock market.

Due to their structural complexities, the attributes of convertibles may vary. Therefore, they are typically categorized as Yield Alternatives represented by the U.S. CV Index (VYLD), Total Return Alternatives represented by the U.S. CV Index (VTOT), or Equity Alternatives represented by the U.S. CV Index (VEQU).

The ICE BofAML Total Return U.S. Convertibles Index is a subset of ICE BofAML All U.S. Convertibles Index including securities with a delta greater than or equal to 0.4 and less than 0.8 (VTOT).

The ICE BofAML Yield Alternative U.S. Convertibles Index (VYLD) is a subset of ICE BofAML All U.S. Convertibles Index including securities with a delta less than 0.4 (exhibiting bond-like characteristics).

The ICE BofAML Equity Alternative U.S. Convertibles Index (VEQU) is a subset of ICE BofAML All U.S. Convertibles Index including securities with a delta of 0.8 and greater (exhibiting stock-like characteristics).

Index returns assume reinvestment of dividends and do not reflect deduction of fees and expenses. It is not possible to invest directly in an index.

contributor. In addition, our lack of participation in the UK assisted return. Conversely, selection in Emerging Asia was detrimental to the Fund’s performance. Specifically, China and Taiwan were leading detractors. In addition, security selection in Europe, the Middle East and Africa (EMEA) lost ground on a relative basis. Positions in Ghana hurt performance, as did our lack of exposure to Russia.

How is the Fund positioned?

We favor balanced convertibles that offer the most attractive opportunity given their combination of upside potential and downside risk mitigation. During the market retreat, we looked to take advantage of convertibles trading at discounts and sought issues poised to capture significant equity upside while also providing downside resilience. The market pullback created an opportunity to revisit several holdings that we had previously sold or trimmed when they had become overly equity sensitive. In addition, wider credit spreads and increased volatility spurred a significant increase in new convertible issues that provided attractive opportunities on a selective basis.

From a sector standpoint, the Fund’s largest weights reside within information technology and consumer discretionary on an absolute basis, while energy and utilities comprise the smallest weights. On a relative basis, the largest industry overweight positions include application software and real estate operating companies. Integrated telecommunication services and specialty chemicals are among the underweight industries.

Allocations to consumer discretionary and health care rose during the period with increased weights in hotels, resorts & cruise lines and health care equipment. By contrast, allocations to energy and financials decreased over the period with reductions to integrated oil & gas and asset management & custody banks.

What are your closing thoughts for Fund shareholders?

Our belief has always been that the flipside of volatility is opportunity and the recent drawdown of the market has provided significant opportunities going forward. We expect convertibles to benefit from narrowing credit spreads, the normalization of equity prices and richening convertible structural valuation. The convertible market has a relatively heavy amount in the growth areas of the market that we view as attractive—particularly in the technology and health care sectors.

We expect to see increased volatility as the global markets continue to sort through coronavirus impacts on all aspects of economic activity. Global monetary policy is extremely accommodative and the major central banks have taken aggressive actions to address the effects of reduced economic activity and high uncertainty. We believe that our focus on continually seeking to improve the overall risk/reward of the portfolio will serve investors well during the potentially challenging and volatile days ahead.

CALAMOS TIMPANI SMALL CAP GROWTH FUND

INVESTMENT TEAM DISCUSSION

How has the Fund performed?

For thesix-month period ended April 30, 2020, Calamos Timpani Small Cap Growth Fund declined-2.04% (Class I shares at net asset value), outperforming the Russell 2000 Growth Index drop of-7.62%.

Since Class I shares inception on March 23, 2011, the Fund has returned 10.33% on an annualized basis, while the Russell 2000 Growth Index returned 8.78% over the same period. We believe these comparisons demonstrate the Fund’s ability to outdistance its benchmark over full market cycles.

What factors influenced performance during the reporting period?

An11-year bull market in equities came to an abrupt halt during the period.COVID-19, which initially was viewed as more regional than global, overtook economics, politics, world health organizations and investors’ psyches. The events, decisions and results, which all had significant influence on Fund and market performance for the period, will be the topic of case studies in history books for years to come. Headlines referenced many “first,” “most” and “fastest” in terms of market history being made. Economic activity plummeted globally as governments mandated shutting down large swaths of their economies to “flatten the curve.” However, governments and central banks around the world also responded quickly with enormous fiscal and monetary relief. Equity markets cratered, as investorsde-risked their portfolios in a sprint for the exits. The equity market dropped 34%, only to see a rapid rebound and 27% gain from market bottom to the end of the reporting period. The VIX Index, a measure of U.S. equity market volatility, began the period with a sanguine reading of 13, but registered an alarming 82 bymid-March 2020. To add to the drama, oil markets went into freefall as the Kingdom of Saudi Arabia and Russia engaged in an unfortunately timed price war, and at one point oil futures’ prices went negative. This was truly a remarkable period.

For the full reporting period, the Fund significantly outperformed the Russell 2000 Growth Index through strong security selection, though sector allocations were modestly additive as well. During the extreme market volatility, management was quite active in managing portfolio holdings. Specifically, we endeavored to improve overall quality by selling names that may have strong growth expectations, but in our view are more likely to fall prey to a skittish and skeptical market in light of economic conditions. In addition, we sought to add to positions that helped balance out cyclical and secular growth opportunities going forward.

The biggest contributors to the Fund’s relative performance were security selection and the overweight to the information technology sector. Fund holdings collectively provided a strongly positive return in technology, while the sector as a whole within the benchmark finished negative. Selection within the application software sector were stalwarts, as companies providing connectivity saw strength owing to the work-from-home andshelter-at-home mandates. Semiconductor and internet services & infrastructure names also saw strong gains. An underweight to the more cyclically oriented industrials sector also provided lift, and our security selection was strongly positive

AVERAGE ANNUAL TOTAL RETURN^† AS OF 4/30/20

Performance data quoted represents past performance, which is no guarantee of future results.Current performance may be lower or higher than the performance quoted. The principal value and investment return of an investment will fluctuate so that your shares, when redeemed, may be worth more or less than their original cost.

As of the prospectus dated 2/28/20, the Fund’s gross expense ratio for Class A shares is 1.38%, Class I shares is 1.14% and Class R6 shares is 1.10%. The Fund’s investment adviser has contractually agreed to reimburse Fund expenses through March 1, 2022, to the extent necessary so that Total Annual Fund Operating Expenses of Class A shares and Class I shares are limited to 1.30% and 1.05% of average net assets, respectively. The Fund’s investment adviser has contractually agreed to limit the Fund’s annual ordinary operating expenses for Class R6 shares (as a percentage of average net assets) to 1.05% less the Fund’s annual sub-transfer agency ratio (the aggregate sub-transfer agency fees of the Fund’s other share classes divided by the aggregate average annual net assets of the Fund’s other share classes). For purposes of these expense limitations, operating expenses do not include taxes, interest, short interest, short dividend expenses, brokerage commissions, acquired fund fees and expenses, and extraordinary expenses, if any. Calamos Advisors may recapture previously waived expense amounts within the same fiscal year for any day where the respective share class’s expense ratio falls below the contractual expense limit up to the expense limit for that day. This undertaking is binding on Calamos Advisors and any of its successors and assigns. This agreement is not terminable by either party. The expense ratios shown above may differ from the more recent expense ratios reported in the Financial Highlights section of this report.

NOTES:

Effective as of the close of business on May 31, 2019, the Fund acquired all of the assets, subject to the liabilities, of the Timpani Small Cap Growth Fund (the “Predecessor Fund”) through a tax-free reorganization (the “Reorganization”). Pursuant to the Reorganization of the Predecessor Fund into the Fund, Class Y shareholders of the Predecessor Fund received Class A shares of the Fund, and Service Class and Institutional Class shareholders of the Predecessor Fund each received Class I shares of the Fund. As a result of the Reorganization, the Fund adopted the performance and financial history of the Predecessor Fund. Accordingly, the performance shown in the average annual total return table above for periods prior to the commencement of the Fund’s operations on June 1, 2019 is the performance of the Predecessor Fund. The Fund has the same investment objective, strategy and portfolio manager as the Predecessor Fund. As a result, the performance of the Fund would have been substantially similar to that of the Predecessor Fund.

The graphs do not reflect the income taxes that you would pay on fund distributions or the redemption of fund shares. Fund performance includes reinvestment of dividends and adjustment for the maximum sales charge for Class A shares. The performance of other classes will vary from the performance of the class shown based on the difference in sales charges and fees paid by shareholders investing in different share classes.

The Russell 2000 Growth Index is a composite of small cap companies located in the U.S. that also exhibit a growth probability.

Index returns assume reinvestment of dividends and do not reflect deduction of fees and expenses. It is not possible to invest directly in an index.

The biggest contributors to the Fund’s relative performance were security selection and the overweight to information technology. Names within the application software sector were stalwarts, as companies providing connectivity saw strength owing to the work-from-home andshelter-at-home mandates. Semiconductor and internet services & infrastructure names also saw strong gains. Security selection within industrials was another robust contributor for the period, and an underweight to the more cyclically oriented sector proved beneficial. Investments in research & consulting services and aerospace & defense delivered strong returns, and avoiding problem areas such as airlines added return. As mentioned previously, we increased fund holdings in industrials during the period in an effort to take advantage of heavily discounted growth opportunities in some cyclical areas.

Security selection in consumer discretionary names was a drag on relative performance. Stock picks in homebuilding struggled during the period, and we trimmed or exited certain investments in the space. Automotive retail also proved a difficult space for the period and detracted from relative performance. A modest overweight position to the energy sector detracted from relative performance during the period, as the energy sector struggled with rapidly declining oil prices and decreased demand. Due to the macro and sector headwinds, securities we sold in favor of better opportunities elsewhere.

How is the Fund positioned?

We remain tilted toward secular growth but have some select exposure to high quality cyclical names as well. We are optimistic with regard to overcoming the health issues,re-opening our economy, and opportunity for strong growth businesses. However, given the macro uncertainty and many moving parts, diversification is especially prudent. The Fund increased its stake in information technology names since the beginning of the period. The sector is the Fund’s largest absolute weight and its largest overweight relative to the benchmark. Information technology stocks themselves represent a diverse mix of secular and cyclical growth. Many of the companies we hold saw increases in customer acquisition, largely due to the increase reliance on technology to complete tasks remotely. The Fund also increased weights to health care, utilities and industrials during the period relative to benchmark weights, providing a mix of secular and cyclical growth opportunities.

What closing thoughts do you have for Fund shareholders?

After the marketsell-off and as government and central bankers introduced measures to help alleviate the self-imposed economic contraction, investors began to prognosticate on the eventual shape of the rebound, using a wide range of letters and shapes as descriptors: V, U, L, square root sign, etc. The thought being that the shape and magnitude of the economic rebound will shape the market leadership moving forward. In light of so much uncertainty, we have added some cyclical growth opportunities to our portfolio of strong and underestimated growth names. Small- tomid-cap stocks, in general, have lacked the attention that their large cap brethren have enjoyed. The small- tomid-cap universe offers the same compelling growth stories and themes the broad market leaders: technology for personal and corporate connectivity, security solutions, as well as health care. All the while, these stocks trade at relative discounts to their large-cap growth peers. We believe that this combination speaks to a great opportunity for investors going forward, no matter the eventual shape of the rebound. We are confident that the efforts of health care companies and the medical community, along with the incredible level of fiscal and monetary support will enable economies and markets to recover, and will reward those business managing to opportunities and needs.

CALAMOS GROWTH FUND

INVESTMENT TEAM DISCUSSION

How has the Fund performed?

For thesix-month period ended April 30, 2020, Calamos Growth Fund returned-1.53% (Class I shares at net asset value) versus the S&P 1500 Growth Index return of 2.88%. By way of comparison, the broad equity market, as measured by the S&P 500 Index, declined-3.16% for the same period.

Since the Class I shares inception on September 18, 1997, the Fund has returned 10.53% on an annualized basis. The S&P 1500 Growth Index, the primary benchmark, returned 7.84% over the same period, and the S&P 500 Index returned 7.09%. We believe these comparisons demonstrate the Fund’s ability to outdistance the growth and broad indexes over full market cycles.

What factors influenced performance over the period?

An11-year bull market in equities came to an abrupt halt during the period.COVID-19, which initially was viewed as more regional than global, overtook economics, politics, world health organizations and investors’ psyches. The events, decisions and results, which all had significant influence on Fund and market performance for the period, will be the topic of case studies in history books for years to come. Headlines referenced many “first,” “most” and “fastest” in terms of market history being made. Economic activity plummeted globally as governments mandated shutting down large swaths of their economies to “flatten the curve.” However, governments and central banks around the world also responded quickly with enormous fiscal and monetary relief. Equity markets cratered, as investorsde-risked their portfolios in a sprint for the exits. The equity market dropped 34%, only to see a rapid rebound and 27% gain from market bottom to the end of the reporting period. The VIX Index, a measure of U.S. equity market volatility, began the period with a sanguine reading of 13, but registered an alarming 82 bymid-March 2020. To add to the drama, oil markets went into freefall as the Kingdom of Saudi Arabia and Russia engaged in an unfortunately timed price war, and at one point oil futures’ prices went negative. This was truly a remarkable period.

Investors showed a clear preference for growth stocks, as the S&P 1500 Growth Index returned 2.88% significantly outpacing the S&P 1500 Value Index’s decline of-12.48%. Many of the businesses that had been leading the U.S. equity market prior toCOVID-19 saw their relative business prospects actually accelerate in light of economic and social conditions. Companies that provide connectivity for working from home, home entertainment, retail delivery, and innovative health care solutions were all market favorites for the period. Within the growth benchmark, information technology (+10%), consumer discretionary (+7%), health care (+7%) and communication services (+6%) all led the market. Energy (-32%) was the biggest laggard, with industrials(-14%), materials(-11%), financials(-10%), real estate(-8%), utilities(-8%) and consumer staples(-5%) also trailing the overall index.

While market leadership was narrow, the Fund benefitted from owning the benchmark index’stop-five contributors as well as thetop-five names by market capitalization. However, overall the Fund lagged the benchmark index largely due to selection among industrial names in aerospace and defense as well as airlines. We believed they had

been able to look through the economic slowdown toward a potential path of recovery. The U.S. government and governments around the world have thrown tremendous amounts of monetary and fiscal policy at the problem, in an effort not to repeat the same mistakes they made responding to the Great Financial Crisis of 2008. Businesses that had footholds in areas that consumers, businesses and governments consider necessary only strengthened their relative positions through this economic and health crisis. While we are not out of the woods yet, society will find a way forward. Despite many risks, such as a second wave of infection or other yet unforeseen obstacles tore-opening our economy, we believe that U.S. growth businesses are attractive investment opportunities in alow-growth,low-interest-rate environment. There may be some cyclical growth opportunities in the near-term, and we have diversified the portfolio to include what we consider some of the best candidates.

CALAMOS GROWTH AND INCOME FUND

INVESTMENT TEAM DISCUSSION

How has the Fund performed?

For thesix-month period ended April 30, 2020, Calamos Growth and Income Fund returned-1.25% (Class I shares at net asset value) versus a drop of-3.16% for the S&P 500 Index, capturing 40% of the equity market’s decline. The ICE BofA All U.S. Convertibles ex Mandatory Index registered a gain of 2.50% for the period. We manage this Fund with the goal of achieving upside equity participation and potential downside risk mitigation over full market cycles. Since its Class I shares inception on September 18, 1997, the Fund gained 9.12% on an annualized basis versus a 7.09% return for the S&P 500 Index and 7.55% return for the ICE BofA All U.S. Convertibles ex Mandatory Index.

Please discuss the Fund’s lower-volatility characteristics.

We believe the Fund’s historical lower-volatility characteristics are a byproduct of our focus on participating in equity market upside with less volatility than the market as a whole. Beta is one popular statistic for measuring volatility. Beta considers a fund’s historic volatility versus the market, which is assigned a beta of 1.0. A fund with half the volatility of the market would have a beta of 0.5, while a fund with a beta of 2.0 would have been twice as volatile as the market. Since its inception, the Fund has had a beta of 0.74 (Class I shares) versus the S&P 500 Index. The Fund, therefore, outperformed the broader equity market, as measured by the S&P 500 Index, with less volatility than the equity market. Please note that past performance does not indicate future results and that beta is one of many measures of risk.

What factors influenced performance during the reporting period?

An11-year bull market in equities came to an abrupt halt during the period.COVID-19, which initially was viewed as more regional than global, overtook economics, politics, world health organizations and investors’ psyches. The events, decisions and results, which all had significant influence on Fund and market performance for the period, will be the topic of case studies in history books for years to come. Headlines referenced many “first,” “most” and “fastest” in terms of market history being made. Economic activity plummeted globally as governments mandated shutting down large swaths of their economies to “flatten the curve.” However, governments and central banks around the world also responded quickly with enormous fiscal and monetary relief. Equity markets cratered, as investorsde-risked their portfolios in a sprint for the exits. The equity market dropped 34%, only to see a rapid rebound and 27% gain from market bottom to the end of the reporting period. The VIX Index, a measure of U.S. equity market volatility, began the period with a sanguine reading of 13, but registered an alarming 82 bymid-March 2020. To add to the drama, oil markets went into freefall as the Kingdom of Saudi Arabia and Russia engaged in an unfortunately timed price war, and at one point oil futures’ prices went negative. This was truly a remarkable period.

Investors showed a clear preference for growth stocks, as the S&P 500 Growth Index returned 4.18%, significantly outpacing the S&P 500 Value Index’s decline of-11.48%. Many of the businesses that had been leading the U.S. equity market prior toCOVID-19 saw their relative business prospects actually accelerate in light of economic and social conditions. Connectivity for working remotely, home entertainment, retail

that have the capital and resources to not only survive, but also thrive in this new paradigm. Health care and safety will be paramount, and businesses that address those needs are attractive in our view. The use of data, connectivity and virtualization are also themes that should benefit going forward long after the pandemic fades.

Please discuss the Fund as a source for income and total distribution yield.

The Fund’s risk-conscious approach and broad investment universe have contributed to an annual distribution history that we believe is compelling. In addition to convertible securities, our team often identifies opportunities in dividend-paying stocks. By investing in these names as well as more growth-oriented stocks, we can pursue a potentially lower-volatility outcome that also supports an attractive distribution stream.

What closing thoughts do you have for Fund shareholders?

In our view, an investment strategy such as Calamos Growth and Income Fund makes the most sense in more volatile markets—although no one could have predicted the turn of events that we have witnessed over the past six months. Investors quicklyde-risked as news flow continued to go increasingly south. However, subsequently, and amazingly quickly, investors were able to incorporate strong government support with diminished growth expectations and move forward once again. Market timing has consistently proven to be difficult at best and requires two extremely well timed decisions. We believe our strategy can help investors worry less about market timing by managing the up and down cycles through our differentiated approach to equity markets. We believe that collectively, we will be able to persevere through this pandemic and, as such, keep an eye toward growth. That said, there are significant potential risks associated with the reopening of global economies, the main danger being a secondary wave of infections. To that end, we will position the portfolio aiming to capture significant equity market opportunities in secular and cyclical growth business, while being mindful of downside resilience as risk management must be a continual focus.

CALAMOS DIVIDEND GROWTH FUND

INVESTMENT TEAM DISCUSSION

How has the Fund performed?

For thesix-month period ended April 30, 2020, Calamos Dividend Growth Fund returned-3.32% (Class I shares at net asset value), performing broadly in line with the S&P 500 Index return of-3.16%. The Fund outperformed the Morningstar Large Blend category average of -5.96% and ranked in the 31st percentile(1-year).*

What factors influenced performance during the reporting period?

An11-year bull market in equities came to an abrupt halt during the period.COVID-19, which initially was viewed as more regional than global, overtook economics, politics, world health organizations and investors’ psyches. The events, decisions and results, which all had significant influence on Fund and market performance for the period, will be the topic of case studies in history books for years to come. Headlines referenced many “first,” “most” and “fastest” in terms of market history being made. Economic activity plummeted globally as governments mandated shutting down large swaths of their economies to “flatten the curve.” However, governments and central banks around the world also responded quickly with enormous fiscal and monetary relief. Equity markets cratered, as investorsde-risked their portfolios in a sprint for the exits. The equity market dropped 34%, only to see a rapid rebound and 27% gain from market bottom to the end of the reporting period. The VIX Index, a measure of U.S. equity market volatility, began the period with a sanguine reading of 13, but registered an alarming 82 bymid-March 2020. To add to the drama, oil markets went into freefall as the Kingdom of Saudi Arabia and Russia engaged in an unfortunately timed price war, and at one point oil futures’ prices went negative. This was truly a remarkable period.

Investors showed a clear preference for growth stocks, with the S&P 500 Growth Index’s 4.18% return significantly outpacing the S&P 500 Value Index decline of-11.48%. Many of the businesses that had been leading the U.S. equity market prior to theCOVID-19 crisis saw their relative business prospects actually accelerate in light of economic and social conditions. Companies that provide connectivity for working from home, home entertainment, retail delivery, and innovative health care solutions were all market favorites for the period. Within the S&P 500 Index, information technology (+11%), health care (+8%), consumer discretionary (+2%), communication services (+1%) and consumer staples(-3%) all led the market. Energy(-30%) was the biggest laggard, with financials(-19%), industrials(-18%), real estate(-12%), utilities(-8%) and materials(-8%) also trailing the overall index.

The Fund benefitted from owning high-quality growth stocks and avoiding more cyclically oriented stocks in the consumer discretionary sector. Selection and an overweight to internet & direct marketing retail was additive to relative performance as current social and economic conditions consolidated many of the advantages businesses had in this arena. Avoiding the struggling luxury goods space also helped within the consumer discretionary sector. Strong security selection and an underweight

AVERAGE ANNUAL TOTAL RETURN^† AS OF 4/30/20

Performance data quoted represents past performance, which is no guarantee of future results.Current performance may be loweror higher than the performance quoted. The principal value and investment return of an investment will fluctuate so that your shares, when redeemed, may be worth more or less than their original cost.

As of the prospectus dated 2/28/20, the Fund’s gross expense ratio for Class A shares is 1.95%, Class C shares is 2.66% and Class I shares is 1.68%. The Fund’s Investment Adviser has contractually agreed to reimburse Fund expenses through 3/1/22 to the extent necessary so that Total Annual Fund Operating Expenses (excluding taxes, interest, short interest, short dividend expenses, brokerage commissions, acquired fund fees and expenses and extraordinary expenses, if any) of Class A, Class C and Class I shares are limited to 1.35%, 2.10%,1.10% of average net assets, respectively. Calamos Advisors may recapture previously waived expense amounts within the same fiscal year for any day where the respective Fund’s expense ratio falls below the contractual expense limit up to the expense limit for that day. This undertaking is binding on Calamos Advisors and any of its successors and assigns. This agreement is not terminable by either party. The expense ratios shown above may differ from the more recent expense ratios reported in the Financial Highlights section of this report.

NOTES:

The graph does not reflect the income taxes that you would pay on fund distributions or the redemption of fund shares. Fund performance includes reinvestment of dividends and adjustment for the maximum sales charge for Class A shares. The performance of other classes will vary from the performance of the class shown based on the difference in sales charges and fees paid by shareholders investing in different share classes.

The S&P 500 Index is an unmanaged index generally considered representative of the U.S. stock market.

Index returns assume reinvestment of dividends and do not reflect deduction of fees and expenses. It is not possible to invest directly in an index.

the period, the Fund increased its allocation to the sector, ending the period with a slight overweight relative to the S&P 500 Index. Health care stocks were also strong contributors to performance, as the sector was clearly favored in light of the pandemic. Fund selection within pharmaceuticals, life sciences & tools, and biotechnology all contributed to Fund performance.

Holdings in financials detracted most from the Fund’s performance during the period, underperforming those of the S&P 500 Index. An overweight to the sector was a drag on performance as well. The financials sector struggled in light of the historic economic slowdown, and Fund holdings in diversified banks and multi-line insurance weighed heavily on performance during the period. An overweight to the cyclically oriented industrials sector and issue selection within the space also detracted from Fund performance. Aerospace & defense names as well as airlines holdings struggled during the period, as global travel slowed to a near standstill. The Fund was very active in the industrials sector during the period, looking to decrease exposures during the marketsell-off and selectively adding to businesses with the potential to benefit as conditions improve.

How is the Fund positioned?

In light of macro conditions, the Fund continues to favor strong, market-share-dominating names that continue to enjoy growth in their businesses. However, as pessimism has weighed heavily on many cyclical growth opportunities, the Fund also has invested in those areas, given the outstanding values. As of the end of the reporting period, the Fund maintained overweights to the consumer discretionary and industrials sectors. The Fund increased its weightings in consumer discretionary names that have been market leaders despite economic conditions. While the Fund’s relative weight to the industrials sector did not change significantly during the period, we did look to add to businesses that could benefit from a cyclical upturn from “bad” to “less bad.” The Fund is underweight to consumer staples and real estate as well. During thesix-month period, the Fund reduced its allocation to consumer staples as many names in the sector became overly favored during the market and economic crisis.

What closing thoughts do you have for Fund shareholders?

We are viewing the economic impact of globalshelter-at-home orders in line with what we have seen from natural disasters such as hurricanes. However, there was nothing usual about the speed and magnitude of the decline in equity markets, so we should not expect to see anything normal about the market’s recovery. The debate going forward appears centered around the contrast of slow growth versus a quicker jump-start from the massive amount of support and stimulus provided by governments and central banks around the world. Many of the high quality growth businesses can and should continue to dominate in light of current economic conditions, and are likely to do well even as some sense of normalcy returns. In addition, investors may have been overly pessimistic with regard to cyclical names that, in our view, should benefit as we make progress as a country and globally against the pandemic.

AVERAGE ANNUAL TOTAL RETURN^† AS OF 4/30/20