| Cover Page | May 31, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | May 31, 2022 |
| 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 | 251 N 1st Avenue |
| Entity Address, Address Line Two | Ste. 200 |
| Entity Address, City or Town | Minneapolis |
| Entity Address, State or Province | MN |
| Entity Address, Postal Zip Code | 55401 |
| Country Region | +1 |
| City Area Code | 651 |
| Local Phone Number | 504 5402 |
| Written Communications | true |
| 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 |
