| Cover Page | Dec. 22, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Dec. 22, 2023 |
| Entity Registrant Name | Sezzle Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-56267 |
| Entity Tax Identification Number | 81-0971660 |
| Entity Address, Address Line One | 700 Nicollet Mall |
| Entity Address, Address Line Two | Suite 640 |
| Entity Address, City or Town | Minneapolis |
| Entity Address, State or Province | MN |
| Entity Address, Postal Zip Code | 55402 |
| Country Region | +1 |
| City Area Code | 651 |
| Local Phone Number | 504 5294 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001662991 |
| Amendment Flag | false |
| Title of 12(b) Security | Common Stock, par value $0.00001 per share |
| Trading Symbol | SEZL |
| Security Exchange Name | NASDAQ |
