Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Document Information [Line Items]
Entity Central Index Key	0001046203
Entity Registrant Name	Guaranty Federal Bancshares Inc
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	0-23325
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	43-1792717
Entity Address, Address Line One	2144 E Republic Rd, 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
Title of 12(b) Security	Common Stock, Par Value $0.10 per share
Trading Symbol	GFED
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		4,385,031