INVESTMENT IN OPERATING PARTNERSHIPS (Details 3) (USD $)	6 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Revenues
Rental	$ 69,790,134		$ 74,753,514
Interest and other	2,076,732		3,083,333
Operating Partnerships Revenues	71,866,866		77,836,847
Expenses
Interest	14,242,842		16,210,932
Depreciation and amortization	20,819,092		21,985,899
Operating expenses	45,719,627		48,484,295
Operating Partnerships Total Expenses	80,781,561		86,681,126
NET INCOME (LOSS)	(8,914,695)		(8,844,279)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(8,825,548)	[1]	(8,755,836)	[1]
Net income (loss) allocated to other Partners	(89,147)		(88,443)
Series Twenty [Member]
Revenues
Rental	1,303,143		2,897,607
Interest and other	31,893		283,027
Operating Partnerships Revenues	1,335,036		3,180,634
Expenses
Interest	206,813		531,654
Depreciation and amortization	331,443		655,309
Operating expenses	950,835		2,143,186
Operating Partnerships Total Expenses	1,489,091		3,330,149
NET INCOME (LOSS)	(154,055)		(149,515)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(152,514)	[2]	(148,020)	[2]
Net income (loss) allocated to other Partners	(1,541)		(1,495)
Series Twenty One [Member]
Revenues
Rental	978,984		1,333,625
Interest and other	15,752		82,197
Operating Partnerships Revenues	994,736		1,415,822
Expenses
Interest	299,552		362,020
Depreciation and amortization	195,476		281,393
Operating expenses	612,778		816,724
Operating Partnerships Total Expenses	1,107,806		1,460,137
NET INCOME (LOSS)	(113,070)		(44,315)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(111,939)	[3]	(43,872)	[3]
Net income (loss) allocated to other Partners	(1,131)		(443)
Series Twenty Two [Member]
Revenues
Rental	1,618,036		2,395,219
Interest and other	37,312		129,429
Operating Partnerships Revenues	1,655,348		2,524,648
Expenses
Interest	261,508		405,068
Depreciation and amortization	538,029		697,822
Operating expenses	1,066,611		1,834,300
Operating Partnerships Total Expenses	1,866,148		2,937,190
NET INCOME (LOSS)	(210,800)		(412,542)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(208,692)	[4]	(408,417)	[4]
Net income (loss) allocated to other Partners	(2,108)		(4,125)
Series Twenty Three [Member]
Revenues
Rental	1,802,156		2,382,379
Interest and other	54,167		111,458
Operating Partnerships Revenues	1,856,323		2,493,837
Expenses
Interest	283,507		442,732
Depreciation and amortization	436,076		587,794
Operating expenses	1,281,812		1,744,974
Operating Partnerships Total Expenses	2,001,395		2,775,500
NET INCOME (LOSS)	(145,072)		(281,663)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(143,620)	[5]	(278,845)	[5]
Net income (loss) allocated to other Partners	(1,452)		(2,818)
Series Twenty Four [Member]
Revenues
Rental	1,336,491		2,221,678
Interest and other	40,317		65,428
Operating Partnerships Revenues	1,376,808		2,287,106
Expenses
Interest	215,653		434,804
Depreciation and amortization	323,206		613,519
Operating expenses	932,790		1,447,719
Operating Partnerships Total Expenses	1,471,649		2,496,042
NET INCOME (LOSS)	(94,841)		(208,936)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(93,893)	[6]	(206,847)	[6]
Net income (loss) allocated to other Partners	(948)		(2,089)
Series Twenty Five [Member]
Revenues
Rental	1,196,777		2,046,833
Interest and other	36,953		123,316
Operating Partnerships Revenues	1,233,730		2,170,149
Expenses
Interest	216,156		375,920
Depreciation and amortization	269,332		526,661
Operating expenses	800,983		1,232,914
Operating Partnerships Total Expenses	1,286,471		2,135,495
NET INCOME (LOSS)	(52,741)		34,654
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(52,214)	[7]	34,307	[7]
Net income (loss) allocated to other Partners	(527)		347
Series Twenty Six [Member]
Revenues
Rental	4,071,227		4,205,557
Interest and other	163,259		153,808
Operating Partnerships Revenues	4,234,486		4,359,365
Expenses
Interest	709,251		759,490
Depreciation and amortization	1,061,857		1,112,812
Operating expenses	2,935,556		3,027,281
Operating Partnerships Total Expenses	4,706,664		4,899,583
NET INCOME (LOSS)	(472,178)		(540,218)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(467,456)	[8]	(534,816)	[8]
Net income (loss) allocated to other Partners	(4,722)		(5,402)
Series Twenty Seven [Member]
Revenues
Rental	2,737,440		2,713,378
Interest and other	35,125		34,622
Operating Partnerships Revenues	2,772,565		2,748,000
Expenses
Interest	649,795		675,977
Depreciation and amortization	666,202		673,396
Operating expenses	1,538,781		1,537,855
Operating Partnerships Total Expenses	2,854,778		2,887,228
NET INCOME (LOSS)	(82,213)		(139,228)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(81,391)	[9]	(137,836)	[9]
Net income (loss) allocated to other Partners	(822)		(1,392)
Series Twenty Eight [Member]
Revenues
Rental	3,585,012		3,727,756
Interest and other	84,283		80,578
Operating Partnerships Revenues	3,669,295		3,808,334
Expenses
Interest	637,897		714,034
Depreciation and amortization	1,001,916		1,068,019
Operating expenses	2,349,128		2,417,205
Operating Partnerships Total Expenses	3,988,941		4,199,258
NET INCOME (LOSS)	(319,646)		(390,924)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(316,450)	[10]	(387,015)	[10]
Net income (loss) allocated to other Partners	(3,196)		(3,909)
Series Twenty Nine [Member]
Revenues
Rental	3,850,616		3,824,944
Interest and other	97,783		180,240
Operating Partnerships Revenues	3,948,399		4,005,184
Expenses
Interest	686,907		686,031
Depreciation and amortization	1,261,391		1,153,479
Operating expenses	2,555,944		2,538,421
Operating Partnerships Total Expenses	4,504,242		4,377,931
NET INCOME (LOSS)	(555,843)		(372,747)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(550,285)	[11]	(369,020)	[11]
Net income (loss) allocated to other Partners	(5,558)		(3,727)
Series Thirty [Member]
Revenues
Rental	2,311,414		2,399,069
Interest and other	37,407		46,776
Operating Partnerships Revenues	2,348,821		2,445,845
Expenses
Interest	352,747		400,847
Depreciation and amortization	500,819		575,697
Operating expenses	1,851,577		1,819,477
Operating Partnerships Total Expenses	2,705,143		2,796,021
NET INCOME (LOSS)	(356,322)		(350,176)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(352,759)	[12]	(346,674)	[12]
Net income (loss) allocated to other Partners	(3,563)		(3,502)
Series Thirty One [Member]
Revenues
Rental	5,201,988		5,322,090
Interest and other	153,227		183,285
Operating Partnerships Revenues	5,355,215		5,505,375
Expenses
Interest	870,089		977,477
Depreciation and amortization	1,475,251		1,460,349
Operating expenses	3,393,982		3,317,803
Operating Partnerships Total Expenses	5,739,322		5,755,629
NET INCOME (LOSS)	(384,107)		(250,254)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(380,266)	[13]	(247,751)	[13]
Net income (loss) allocated to other Partners	(3,841)		(2,503)
Series Thirty Two [Member]
Revenues
Rental	2,952,526		2,874,786
Interest and other	93,316		165,326
Operating Partnerships Revenues	3,045,842		3,040,112
Expenses
Interest	615,329		624,777
Depreciation and amortization	1,080,867		1,077,939
Operating expenses	1,973,481		1,931,278
Operating Partnerships Total Expenses	3,669,677		3,633,994
NET INCOME (LOSS)	(623,835)		(593,882)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(617,597)	[14]	(587,943)	[14]
Net income (loss) allocated to other Partners	(6,238)		(5,939)
Series Thirty Three [Member]
Revenues
Rental	1,385,439		1,429,455
Interest and other	57,389		44,560
Operating Partnerships Revenues	1,442,828		1,474,015
Expenses
Interest	342,440		368,860
Depreciation and amortization	462,972		498,368
Operating expenses	848,584		907,168
Operating Partnerships Total Expenses	1,653,996		1,774,396
NET INCOME (LOSS)	(211,168)		(300,381)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(209,056)	[15]	(297,377)	[15]
Net income (loss) allocated to other Partners	(2,112)		(3,004)
Series Thirty Four [Member]
Revenues
Rental	2,917,703		3,144,252
Interest and other	104,826		122,868
Operating Partnerships Revenues	3,022,529		3,267,120
Expenses
Interest	516,409		641,513
Depreciation and amortization	1,021,332		1,118,144
Operating expenses	2,029,267		2,072,518
Operating Partnerships Total Expenses	3,567,008		3,832,175
NET INCOME (LOSS)	(544,479)		(565,055)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(539,034)	[16]	(559,404)	[16]
Net income (loss) allocated to other Partners	(5,445)		(5,651)
Series Thirty Five [Member]
Revenues
Rental	2,315,842		2,374,727
Interest and other	72,577		87,845
Operating Partnerships Revenues	2,388,419		2,462,572
Expenses
Interest	483,187		617,470
Depreciation and amortization	777,325		865,354
Operating expenses	1,486,188		1,575,107
Operating Partnerships Total Expenses	2,746,700		3,057,931
NET INCOME (LOSS)	(358,281)		(595,359)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(354,698)	[17]	(589,405)	[17]
Net income (loss) allocated to other Partners	(3,583)		(5,954)
Series Thirty Six [Member]
Revenues
Rental	1,799,791		1,754,480
Interest and other	31,712		42,693
Operating Partnerships Revenues	1,831,503		1,797,173
Expenses
Interest	420,728		391,918
Depreciation and amortization	508,551		505,895
Operating expenses	1,090,699		1,081,491
Operating Partnerships Total Expenses	2,019,978		1,979,304
NET INCOME (LOSS)	(188,475)		(182,131)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(186,590)	[18]	(180,310)	[18]
Net income (loss) allocated to other Partners	(1,885)		(1,821)
Series Thirty Seven [Member]
Revenues
Rental	2,204,612		2,292,014
Interest and other	58,721		84,348
Operating Partnerships Revenues	2,263,333		2,376,362
Expenses
Interest	350,253		348,250
Depreciation and amortization	798,698		811,178
Operating expenses	1,685,515		1,550,036
Operating Partnerships Total Expenses	2,834,466		2,709,464
NET INCOME (LOSS)	(571,133)		(333,102)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(565,422)	[19]	(329,771)	[19]
Net income (loss) allocated to other Partners	(5,711)		(3,331)
Series Thirty Eight [Member]
Revenues
Rental	1,778,084		1,731,327
Interest and other	57,406		69,240
Operating Partnerships Revenues	1,835,490		1,800,567
Expenses
Interest	390,119		393,065
Depreciation and amortization	565,349		560,744
Operating expenses	1,172,684		1,122,693
Operating Partnerships Total Expenses	2,128,152		2,076,502
NET INCOME (LOSS)	(292,662)		(275,935)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(289,735)	[20]	(273,176)	[20]
Net income (loss) allocated to other Partners	(2,927)		(2,759)
Series Thirty Nine [Member]
Revenues
Rental	1,269,984		1,266,157
Interest and other	68,741		72,126
Operating Partnerships Revenues	1,338,725		1,338,283
Expenses
Interest	252,981		256,821
Depreciation and amortization	472,842		473,790
Operating expenses	929,317		910,871
Operating Partnerships Total Expenses	1,655,140		1,641,482
NET INCOME (LOSS)	(316,415)		(303,199)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(313,251)	[21]	(300,167)	[21]
Net income (loss) allocated to other Partners	(3,164)		(3,032)
Series Forty [Member]
Revenues
Rental	2,266,819		2,084,641
Interest and other	51,684		70,286
Operating Partnerships Revenues	2,318,503		2,154,927
Expenses
Interest	453,141		462,522
Depreciation and amortization	689,848		664,779
Operating expenses	1,448,747		1,297,740
Operating Partnerships Total Expenses	2,591,736		2,425,041
NET INCOME (LOSS)	(273,233)		(270,114)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(270,501)	[22]	(267,413)	[22]
Net income (loss) allocated to other Partners	(2,732)		(2,701)
Series Forty One [Member]
Revenues
Rental	2,793,187		2,624,350
Interest and other	79,611		74,064
Operating Partnerships Revenues	2,872,798		2,698,414
Expenses
Interest	622,871		731,683
Depreciation and amortization	1,107,541		754,197
Operating expenses	1,551,998		1,544,093
Operating Partnerships Total Expenses	3,282,410		3,029,973
NET INCOME (LOSS)	(409,612)		(331,559)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(405,516)	[23]	(328,243)	[23]
Net income (loss) allocated to other Partners	(4,096)		(3,316)
Series Forty Two [Member]
Revenues
Rental	3,047,916		3,041,772
Interest and other	114,340		136,146
Operating Partnerships Revenues	3,162,256		3,177,918
Expenses
Interest	674,995		732,891
Depreciation and amortization	878,519		839,248
Operating expenses	1,825,476		1,766,486
Operating Partnerships Total Expenses	3,378,990		3,338,625
NET INCOME (LOSS)	(216,734)		(160,707)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(214,567)	[24]	(159,100)	[24]
Net income (loss) allocated to other Partners	(2,167)		(1,607)
Series Forty Three [Member]
Revenues
Rental	3,693,092		3,407,377
Interest and other	103,602		131,870
Operating Partnerships Revenues	3,796,694		3,539,247
Expenses
Interest	731,762		778,746
Depreciation and amortization	1,159,738		1,066,580
Operating expenses	2,258,417		2,117,673
Operating Partnerships Total Expenses	4,149,917		3,962,999
NET INCOME (LOSS)	(353,223)		(423,752)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(349,691)	[25]	(419,514)	[25]
Net income (loss) allocated to other Partners	(3,532)		(4,238)
Series Forty Four [Member]
Revenues
Rental	3,714,834		3,917,597
Interest and other	144,099		123,470
Operating Partnerships Revenues	3,858,933		4,041,067
Expenses
Interest	1,207,246		1,285,764
Depreciation and amortization	1,128,476		1,199,517
Operating expenses	2,312,790		2,239,377
Operating Partnerships Total Expenses	4,648,512		4,724,658
NET INCOME (LOSS)	(789,579)		(683,591)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(781,683)	[26]	(676,755)	[26]
Net income (loss) allocated to other Partners	(7,896)		(6,836)
Series Forty Five [Member]
Revenues
Rental	4,948,081		4,707,400
Interest and other	158,918		272,178
Operating Partnerships Revenues	5,106,999		4,979,578
Expenses
Interest	1,124,478		1,118,720
Depreciation and amortization	1,415,611		1,446,924
Operating expenses	3,126,069		2,824,557
Operating Partnerships Total Expenses	5,666,158		5,390,201
NET INCOME (LOSS)	(559,159)		(410,623)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(553,567)	[27]	(406,517)	[27]
Net income (loss) allocated to other Partners	(5,592)		(4,406)
Series Forty Six [Member]
Revenues
Rental	2,708,940		2,633,044
Interest and other	92,312		112,149
Operating Partnerships Revenues	2,801,252		2,745,193
Expenses
Interest	667,028		691,878
Depreciation and amortization	690,425		696,992
Operating expenses	1,709,618		1,665,348
Operating Partnerships Total Expenses	3,067,071		3,054,218
NET INCOME (LOSS)	(265,819)		(309,025)
Net income (loss) allocated to Boston Capital Tax Credit Fund IV L.P.	(263,161)		(305,935)
Net income (loss) allocated to other Partners	$ (2,658)		$ (3,090)

[1] Amounts include $(7,448,884) and $(6,558,452) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[2] Amounts include $(152,514) and $(148,020) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[3] Amounts include $(111,939) and $(43,872) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[4] Amounts include $(208,692) and $(408,417) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[5] Amounts include $(143,620) and $(278,845) for 2012 and 2011, of net income (loss) not recognized under the equity method of accounting.

[6] Amounts include $(93,893) and $(206,847) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[7] Amounts include $(52,214) and $34,307 for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[8] Amounts include $(467,456) and $(534,816) for 2012 and 2011, respectively, of loss not recognized under the equity method of accounting.

[9] Amounts include $(81,391) and $(137,836) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[10] Amounts include $(316,450) and $(387,015) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[11] Amounts include $(550,285) and $(369,020) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[12] Amounts include $(352,759) and $(346,674) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[13] Amounts include $(380,266) and $(247,751) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[14] Amounts include $(617,597) and $(535,149) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[15] Amounts include $(209,056) and $(297,377) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[16] Amounts include $(539,034) and $(559,404) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[17] Amounts include $(354,698) and $(495,914) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[18] Amounts include $(186,590) and $(126,262) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[19] Amounts include $(565,422) and $(435,185) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[20] Amounts include $(264,962) and $(160,779) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[21] Amounts include $(227,903) and $(245,409) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[22] Amounts include $(168,169) and $(33,040) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[23] Amounts include $(187,046) and $(16,139) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[24] Amounts include $(197,429) and $(125,747) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[25] Amounts include $(206,714) and $(163,996) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[26] Amounts include $(621,862) and $(275,364) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.

[27] Amounts include $(190,923) and $(13,881) for 2012 and 2011, respectively, of net income (loss) not recognized under the equity method of accounting.