INVESTMENTS IN OPERATING PARTNERSHIPS (Details 3) (USD $)	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Revenues
Rental	$ 84,528,316		$ 96,775,255
Interest and other	2,606,962		2,880,833
Operating Partnerships Revenues	87,135,278		99,656,088
Expenses
Interest	15,228,667		18,485,614
Depreciation and amortization	24,157,120		28,740,657
Operating expenses	57,109,285		63,677,809
Operating Partnerships Total Expenses	96,495,072		110,904,080
NET LOSS	(9,359,794)		(11,247,992)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(9,266,195)	[1]	(11,135,514)	[1]
Net loss allocated to other Partners	(93,599)		(112,478)
Series Twenty [Member]
Revenues
Rental	1,126,789		1,613,365
Interest and other	39,437		47,810
Operating Partnerships Revenues	1,166,226		1,661,175
Expenses
Interest	206,097		304,573
Depreciation and amortization	314,858		410,115
Operating expenses	893,788		1,237,697
Operating Partnerships Total Expenses	1,414,743		1,952,385
NET LOSS	(248,517)		(291,210)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(246,032)	[2]	(288,298)	[2]
Net loss allocated to other Partners	(2,485)		(2,912)
Series Twenty One [Member]
Revenues
Rental	1,383,390		1,420,425
Interest and other	17,805		17,811
Operating Partnerships Revenues	1,401,195		1,438,236
Expenses
Interest	379,112		391,381
Depreciation and amortization	245,466		255,973
Operating expenses	825,426		793,317
Operating Partnerships Total Expenses	1,450,004		1,440,671
NET LOSS	(48,809)		(2,435)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(48,321)	[3]	(2,411)	[3]
Net loss allocated to other Partners	(488)		(24)
Series Twenty Two [Member]
Revenues
Rental	1,092,137		1,317,171
Interest and other	25,007		29,434
Operating Partnerships Revenues	1,117,144		1,346,605
Expenses
Interest	178,309		221,714
Depreciation and amortization	247,965		307,676
Operating expenses	766,413		1,005,560
Operating Partnerships Total Expenses	1,192,687		1,534,950
NET LOSS	(75,543)		(188,345)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(74,788)	[4]	(186,462)	[4]
Net loss allocated to other Partners	(755)		(1,883)
Series Twenty Three [Member]
Revenues
Rental	2,258,175		2,304,215
Interest and other	86,400		87,030
Operating Partnerships Revenues	2,344,575		2,391,245
Expenses
Interest	324,093		378,293
Depreciation and amortization	481,712		516,305
Operating expenses	1,667,454		1,807,637
Operating Partnerships Total Expenses	2,473,259		2,702,235
NET LOSS	(128,684)		(310,990)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(127,396)	[5]	(307,879)	[5]
Net loss allocated to other Partners	(1,288)		(3,111)
Series Twenty Four [Member]
Revenues
Rental	866,217		1,240,112
Interest and other	15,078		26,262
Operating Partnerships Revenues	881,295		1,266,374
Expenses
Interest	103,898		164,731
Depreciation and amortization	247,426		367,577
Operating expenses	661,395		891,845
Operating Partnerships Total Expenses	1,012,719		1,424,153
NET LOSS	(131,424)		(157,779)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(130,110)	[6]	(156,201)	[6]
Net loss allocated to other Partners	(1,314)		(1,578)
Series Twenty Five [Member]
Revenues
Rental	705,170		990,490
Interest and other	17,671		19,601
Operating Partnerships Revenues	722,841		1,010,091
Expenses
Interest	114,272		161,238
Depreciation and amortization	154,334		231,048
Operating expenses	510,224		700,334
Operating Partnerships Total Expenses	778,830		1,092,620
NET LOSS	(55,989)		(82,529)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(55,429)	[7]	(81,704)	[7]
Net loss allocated to other Partners	(560)		(825)
Series Twenty Six [Member]
Revenues
Rental	2,421,312		3,703,623
Interest and other	53,260		147,975
Operating Partnerships Revenues	2,474,572		3,851,598
Expenses
Interest	345,108		596,996
Depreciation and amortization	738,393		1,123,521
Operating expenses	1,859,339		2,668,090
Operating Partnerships Total Expenses	2,942,840		4,388,607
NET LOSS	(468,268)		(537,009)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(463,585)	[8]	(531,639)	[8]
Net loss allocated to other Partners	(4,683)		(5,370)
Series Twenty Seven [Member]
Revenues
Rental	3,219,944		3,750,599
Interest and other	53,825		51,588
Operating Partnerships Revenues	3,273,769		3,802,187
Expenses
Interest	688,139		794,729
Depreciation and amortization	713,428		877,750
Operating expenses	1,987,064		2,165,755
Operating Partnerships Total Expenses	3,388,631		3,838,234
NET LOSS	(114,862)		(36,047)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(113,713)	[9]	(35,687)	[9]
Net loss allocated to other Partners	(1,149)		(360)
Series Twenty Eight [Member]
Revenues
Rental	2,925,832		5,116,918
Interest and other	64,124		104,188
Operating Partnerships Revenues	2,989,956		5,221,106
Expenses
Interest	364,909		786,405
Depreciation and amortization	930,537		1,439,859
Operating expenses	2,078,136		3,364,407
Operating Partnerships Total Expenses	3,373,582		5,590,671
NET LOSS	(383,626)		(369,565)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(379,790)	[10]	(365,869)	[10]
Net loss allocated to other Partners	(3,836)		(3,696)
Series Twenty Nine [Member]
Revenues
Rental	3,722,622		5,180,534
Interest and other	133,297		147,493
Operating Partnerships Revenues	3,855,919		5,328,027
Expenses
Interest	679,203		904,271
Depreciation and amortization	1,215,896		1,699,327
Operating expenses	2,586,209		3,478,206
Operating Partnerships Total Expenses	4,481,308		6,081,804
NET LOSS	(625,389)		(753,777)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(619,135)	[11]	(746,239)	[11]
Net loss allocated to other Partners	(6,254)		(7,538)
Series Thirty [Member]
Revenues
Rental	3,192,127		3,414,053
Interest and other	55,254		68,890
Operating Partnerships Revenues	3,247,381		3,482,943
Expenses
Interest	384,121		450,721
Depreciation and amortization	662,354		786,745
Operating expenses	2,585,846		2,722,588
Operating Partnerships Total Expenses	3,632,321		3,960,054
NET LOSS	(384,940)		(477,111)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(381,091)	[12]	(472,340)	[12]
Net loss allocated to other Partners	(3,849)		(4,771)
Series Thirty One [Member]
Revenues
Rental	6,725,282		7,449,157
Interest and other	405,417		277,703
Operating Partnerships Revenues	7,130,699		7,726,860
Expenses
Interest	906,655		1,086,482
Depreciation and amortization	1,874,447		2,183,640
Operating expenses	4,775,906		5,006,692
Operating Partnerships Total Expenses	7,557,008		8,276,814
NET LOSS	(426,309)		(549,954)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(422,046)	[13]	(544,454)	[13]
Net loss allocated to other Partners	(4,263)		(5,500)
Series Thirty Two [Member]
Revenues
Rental	3,988,072		4,360,111
Interest and other	129,477		160,277
Operating Partnerships Revenues	4,117,549		4,520,388
Expenses
Interest	752,380		836,418
Depreciation and amortization	1,518,849		1,589,992
Operating expenses	2,694,721		2,940,274
Operating Partnerships Total Expenses	4,965,950		5,366,684
NET LOSS	(848,401)		(846,296)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(839,917)	[14]	(837,833)	[14]
Net loss allocated to other Partners	(8,484)		(8,463)
Series Thirty Three [Member]
Revenues
Rental	2,123,488		2,100,677
Interest and other	73,152		92,338
Operating Partnerships Revenues	2,196,640		2,193,015
Expenses
Interest	424,090		444,559
Depreciation and amortization	677,718		667,600
Operating expenses	1,355,246		1,308,069
Operating Partnerships Total Expenses	2,457,054		2,420,228
NET LOSS	(260,414)		(227,213)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(257,810)	[15]	(224,941)	[15]
Net loss allocated to other Partners	(2,604)		(2,272)
Series Thirty Four [Member]
Revenues
Rental	3,485,018		4,320,147
Interest and other	105,571		135,796
Operating Partnerships Revenues	3,590,589		4,455,943
Expenses
Interest	509,906		636,784
Depreciation and amortization	1,126,273		1,408,564
Operating expenses	2,350,903		2,888,848
Operating Partnerships Total Expenses	3,987,082		4,934,196
NET LOSS	(396,493)		(478,253)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(392,528)	[16]	(473,470)	[16]
Net loss allocated to other Partners	(3,965)		(4,783)
Series Thirty Five [Member]
Revenues
Rental	3,328,568		3,321,007
Interest and other	120,067		111,336
Operating Partnerships Revenues	3,448,635		3,432,343
Expenses
Interest	588,697		601,131
Depreciation and amortization	1,066,886		1,065,218
Operating expenses	2,034,729		2,058,703
Operating Partnerships Total Expenses	3,690,312		3,725,052
NET LOSS	(241,677)		(292,709)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(239,260)	[17]	(289,782)	[17]
Net loss allocated to other Partners	(2,417)		(2,927)
Series Thirty Six [Member]
Revenues
Rental	2,155,046		2,226,451
Interest and other	46,180		54,862
Operating Partnerships Revenues	2,201,226		2,281,313
Expenses
Interest	396,753		422,755
Depreciation and amortization	697,265		681,862
Operating expenses	1,514,535		1,486,517
Operating Partnerships Total Expenses	2,608,553		2,591,134
NET LOSS	(407,327)		(309,821)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(403,254)	[18]	(306,723)	[18]
Net loss allocated to other Partners	(4,073)		(3,098)
Series Thirty Seven [Member]
Revenues
Rental	3,324,764		3,425,506
Interest and other	81,492		89,176
Operating Partnerships Revenues	3,406,256		3,514,682
Expenses
Interest	529,618		534,400
Depreciation and amortization	1,152,618		1,186,940
Operating expenses	2,535,651		2,482,082
Operating Partnerships Total Expenses	4,217,887		4,203,422
NET LOSS	(811,631)		(688,740)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(803,515)	[19]	(681,853)	[19]
Net loss allocated to other Partners	(8,116)		(6,887)
Series Thirty Eight [Member]
Revenues
Rental	2,845,162		2,742,355
Interest and other	76,509		64,713
Operating Partnerships Revenues	2,921,671		2,807,068
Expenses
Interest	536,192		545,786
Depreciation and amortization	760,700		791,171
Operating expenses	1,925,633		1,776,638
Operating Partnerships Total Expenses	3,222,525		3,113,595
NET LOSS	(300,854)		(306,527)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(297,845)	[20]	(303,462)	[20]
Net loss allocated to other Partners	(3,009)		(3,065)
Series Thirty Nine [Member]
Revenues
Rental	2,083,504		2,051,267
Interest and other	73,611		74,127
Operating Partnerships Revenues	2,157,115		2,125,394
Expenses
Interest	373,445		381,191
Depreciation and amortization	584,386		658,304
Operating expenses	1,498,867		1,419,540
Operating Partnerships Total Expenses	2,456,698		2,459,035
NET LOSS	(299,583)		(333,641)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(296,587)	[21]	(330,305)	[21]
Net loss allocated to other Partners	(2,996)		(3,336)
Series Forty [Member]
Revenues
Rental	3,105,312		3,077,919
Interest and other	172,029		74,743
Operating Partnerships Revenues	3,277,341		3,152,662
Expenses
Interest	601,716		680,754
Depreciation and amortization	1,017,484		989,733
Operating expenses	2,074,246		2,119,148
Operating Partnerships Total Expenses	3,693,446		3,789,635
NET LOSS	(416,105)		(636,973)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(411,944)	[22]	(630,603)	[22]
Net loss allocated to other Partners	(4,161)		(6,370)
Series Forty One [Member]
Revenues
Rental	4,306,456		4,184,645
Interest and other	123,671		109,707
Operating Partnerships Revenues	4,430,127		4,294,352
Expenses
Interest	922,181		875,912
Depreciation and amortization	1,088,288		1,676,222
Operating expenses	2,689,541		2,391,198
Operating Partnerships Total Expenses	4,700,010		4,943,332
NET LOSS	(269,883)		(648,980)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(267,184)	[23]	(642,490)	[23]
Net loss allocated to other Partners	(2,699)		(6,490)
Series Forty Two [Member]
Revenues
Rental	4,744,893		4,642,261
Interest and other	183,231		151,839
Operating Partnerships Revenues	4,928,124		4,794,100
Expenses
Interest	918,112		962,345
Depreciation and amortization	1,246,081		1,308,459
Operating expenses	2,905,856		2,799,018
Operating Partnerships Total Expenses	5,070,049		5,069,822
NET LOSS	(141,925)		(275,722)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(140,506)	[24]	(272,965)	[24]
Net loss allocated to other Partners	(1,419)		(2,757)
Series Forty Three [Member]
Revenues
Rental	5,790,207		5,716,863
Interest and other	158,764		178,429
Operating Partnerships Revenues	5,948,971		5,895,292
Expenses
Interest	1,023,421		1,102,099
Depreciation and amortization	1,671,650		1,712,649
Operating expenses	3,514,228		3,372,052
Operating Partnerships Total Expenses	6,209,299		6,186,800
NET LOSS	(260,328)		(291,508)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(257,725)	[25]	(288,593)	[25]
Net loss allocated to other Partners	(2,603)		(2,915)
Series Forty Four [Member]
Revenues
Rental	4,445,309		5,846,657
Interest and other	124,497		211,036
Operating Partnerships Revenues	4,569,806		6,057,693
Expenses
Interest	1,217,198		1,776,274
Depreciation and amortization	1,144,382		1,725,913
Operating expenses	2,494,479		3,431,350
Operating Partnerships Total Expenses	4,856,059		6,933,537
NET LOSS	(286,253)		(875,844)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(283,390)	[26]	(867,086)	[26]
Net loss allocated to other Partners	(2,863)		(8,758)
Series Forty Five [Member]
Revenues
Rental	5,054,228		7,151,010
Interest and other	116,481		191,009
Operating Partnerships Revenues	5,170,709		7,342,019
Expenses
Interest	818,545		1,511,863
Depreciation and amortization	1,515,556		2,080,236
Operating expenses	3,469,402		4,598,368
Operating Partnerships Total Expenses	5,803,503		8,190,467
NET LOSS	(632,794)		(848,448)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(626,466)	[27]	(839,964)	[27]
Net loss allocated to other Partners	(6,328)		(8,484)
Series Forty Six [Member]
Revenues
Rental	4,109,292		4,107,717
Interest and other	55,655		155,660
Operating Partnerships Revenues	4,164,947		4,263,377
Expenses
Interest	942,497		931,809
Depreciation and amortization	1,062,168		998,258
Operating expenses	2,854,048		2,763,876
Operating Partnerships Total Expenses	4,858,713		4,693,943
NET LOSS	(693,766)		(430,566)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(686,828)	[28]	(426,261)	[28]
Net loss allocated to other Partners	$ (6,938)		$ (4,305)

[1] Amounts include $(8,555,691) and $(9,717,981) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[2] Amounts include $(246,032) and $(288,298) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[3] Amounts include $(48,321) and $(2,411) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[4] Amounts include $(74,788) and $(186,462) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[5] Amounts include $(127,396) and $(307,879) for 2014 and 2013, of net loss not recognized under the equity method of accounting.

[6] Amounts include $(130,110) and $(156,201) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[7] Amounts include $(55,429) and $(81,704) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[8] Amounts include $(463,585) and $(531,639) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[9] Amounts include $(113,713) and $(35,687) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[10] Amounts include $(379,790) and $(365,869) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[11] Amounts include $(619,135) and $(746,239) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[12] Amounts include $(381,091) and $(472,340) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[13] Amounts include $(422,046) and $(544,454) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[14] Amounts include $(839,917) and $(837,833) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[15] Amounts include $(257,810) and $(224,941) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[16] Amounts include $(392,528) and $(473,470) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[17] Amounts include $(239,260) and $(289,782) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[18] Amounts include $(403,254) and $(306,723) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[19] Amounts include $(803,515) and $(681,853) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[20] Amounts include $(297,845) and $(303,462) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[21] Amounts include $(296,587) and $(330,305) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[22] Amounts include $(411,944) and $(630,603) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[23] Amounts include $(267,184) and $(642,490) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[24] Amounts include $(140,506) and $(165,552) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[25] Amounts include $(244,034) and $(42,243) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[26] Amounts include $(283,390) and $(764,573) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[27] Amounts include $(361,342) and $(304,968) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[28] Amounts include $(255,139) and $- for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.