Document And Entity Information	6 Months Ended
	Sep. 30, 2019 shares
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Registrant Name	BOSTON CAPITAL TAX CREDIT FUND III L P
Entity Central Index Key	0000879555
Current Fiscal Year End Date	--03-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding	0
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	true