| Document And Entity Information | Jan. 21, 2021 |
| Document Information [Line Items] | |
| Entity, Registrant Name | Guaranty Federal Bancshares, Inc. |
| Document, Type | 8-K |
| Document, Period End Date | Jan. 21, 2021 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 0-23325 |
| Entity, Tax Identification Number | 43-1792717 |
| Entity, Address, Address Line One | 2144 E Republic Road, Suite F200 |
| Entity, Address, City or Town | Springfield |
| Entity, Address, State or Province | MO |
| Entity, Address, Postal Zip Code | 65804 |
| City Area Code | 833 |
| Local Phone Number | 875-2492 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | GFED |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0001046203 |
