| Cover | Aug. 05, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 12, 2024 |
| Entity Registrant Name | EXAGEN INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-39049 |
| Entity Tax Identification Number | 20-0434866 |
| Entity Address, Address Line One | 1261 Liberty Way |
| Entity Address, City or Town | Vista |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92081 |
| City Area Code | 760 |
| Local Phone Number | 560-1501 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.001 per share |
| Trading Symbol | XGN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001274737 |
| Amendment Flag | false |
