DOCUMENT AND ENTITY INFORMATION	9 Months Ended
	Dec. 31, 2011
Entity Registrant Name	BOSTON CAPITAL TAX CREDIT FUND IV LP
Entity Central Index Key	0000913778
Current Fiscal Year End Date	--03-31
Entity Filer Category	Smaller Reporting Company
Trading Symbol	BCTC IV
Entity Common Stock, Shares Outstanding	0
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2011
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2012