Document And Entity Information	9 Months Ended
	Dec. 31, 2015 shares
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q3
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
Entity Common Stock, Shares Outstanding	0