DOCUMENT AND ENTITY INFORMATION	6 Months Ended
	Sep. 30, 2012
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
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2012
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2013