INVESTMENTS IN OPERATING PARTNERSHIPS (Details 3) - USD ($)		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015
Revenues
Rental		$ 36,065,499	$ 45,203,563
Interest and other		1,352,575	1,285,405
Operating Partnerships Revenues		37,418,074	46,488,968
Expenses
Interest		6,268,686	7,888,032
Depreciation and amortization		9,906,888	12,463,273
Operating expenses		26,167,804	30,752,781
Operating Partnerships Total Expenses		42,343,378	51,104,086
NET LOSS		(4,925,304)	(4,615,118)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[1]	(4,876,047)	(4,568,964)
Net loss allocated to other Partners		(49,257)	(46,154)
Series Twenty [Member]
Revenues
Rental		334,521	418,810
Interest and other		17,848	19,006
Operating Partnerships Revenues		352,369	437,816
Expenses
Interest		36,427	47,011
Depreciation and amortization		86,616	101,632
Operating expenses		256,689	310,583
Operating Partnerships Total Expenses		379,732	459,226
NET LOSS		(27,363)	(21,410)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[2]	(27,089)	(21,196)
Net loss allocated to other Partners		(274)	(214)
Series Twenty One [Member]
Revenues
Rental		254,448	315,338
Interest and other		1,593	2,100
Operating Partnerships Revenues		256,041	317,438
Expenses
Interest		26,001	44,646
Depreciation and amortization		41,517	51,789
Operating expenses		189,063	244,856
Operating Partnerships Total Expenses		256,581	341,291
NET LOSS		(540)	(23,853)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[3]	(535)	(23,614)
Net loss allocated to other Partners		(5)	(239)
Series Twenty Two [Member]
Revenues
Rental		253,512	475,615
Interest and other		9,919	11,730
Operating Partnerships Revenues		263,431	487,345
Expenses
Interest		26,537	66,701
Depreciation and amortization		55,366	113,609
Operating expenses		215,687	349,376
Operating Partnerships Total Expenses		297,590	529,686
NET LOSS		(34,159)	(42,341)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[4]	(33,817)	(41,918)
Net loss allocated to other Partners		(342)	(423)
Series Twenty Three [Member]
Revenues
Rental		984,595	1,377,593
Interest and other		32,230	42,646
Operating Partnerships Revenues		1,016,825	1,420,239
Expenses
Interest		89,603	157,010
Depreciation and amortization		307,885	324,218
Operating expenses		804,619	1,095,569
Operating Partnerships Total Expenses		1,202,107	1,576,797
NET LOSS		(185,282)	(156,558)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[5]	(183,428)	(154,991)
Net loss allocated to other Partners		(1,854)	(1,567)
Series Twenty Four [Member]
Revenues
Rental		515,358	502,834
Interest and other		9,973	10,154
Operating Partnerships Revenues		525,331	512,988
Expenses
Interest		46,052	47,306
Depreciation and amortization		136,278	137,080
Operating expenses		410,197	418,156
Operating Partnerships Total Expenses		592,527	602,542
NET LOSS		(67,196)	(89,554)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[6]	(66,524)	(88,658)
Net loss allocated to other Partners		(672)	(896)
Series Twenty Five [Member]
Revenues
Rental		427,000	434,822
Interest and other		12,744	10,457
Operating Partnerships Revenues		439,744	445,279
Expenses
Interest		55,151	68,232
Depreciation and amortization		78,604	77,664
Operating expenses		328,546	316,742
Operating Partnerships Total Expenses		462,301	462,638
NET LOSS		(22,557)	(17,359)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[7]	(22,331)	(17,185)
Net loss allocated to other Partners		(226)	(174)
Series Twenty Six [Member]
Revenues
Rental		1,133,662	1,307,218
Interest and other		24,802	25,613
Operating Partnerships Revenues		1,158,464	1,332,831
Expenses
Interest		181,864	197,728
Depreciation and amortization		288,199	352,022
Operating expenses		1,002,380	1,039,030
Operating Partnerships Total Expenses		1,472,443	1,588,780
NET LOSS		(313,979)	(255,949)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[8]	(310,839)	(253,390)
Net loss allocated to other Partners		(3,140)	(2,559)
Series Twenty Seven [Member]
Revenues
Rental		1,380,003	2,131,992
Interest and other		6,276	23,304
Operating Partnerships Revenues		1,386,279	2,155,296
Expenses
Interest		239,810	427,512
Depreciation and amortization		309,373	446,408
Operating expenses		944,846	1,293,531
Operating Partnerships Total Expenses		1,494,029	2,167,451
NET LOSS		(107,750)	(12,155)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[9]	(106,672)	(12,033)
Net loss allocated to other Partners		(1,078)	(122)
Series Twenty Eight [Member]
Revenues
Rental		500,121	1,068,294
Interest and other		9,336	22,268
Operating Partnerships Revenues		509,457	1,090,562
Expenses
Interest		71,995	85,171
Depreciation and amortization		115,386	354,444
Operating expenses		433,166	847,019
Operating Partnerships Total Expenses		620,547	1,286,634
NET LOSS		(111,090)	(196,072)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[10]	(109,979)	(194,111)
Net loss allocated to other Partners		(1,111)	(1,961)
Series Twenty Nine [Member]
Revenues
Rental		962,895	1,003,232
Interest and other		63,597	64,239
Operating Partnerships Revenues		1,026,492	1,067,471
Expenses
Interest		199,552	189,364
Depreciation and amortization		244,583	274,358
Operating expenses		770,811	797,043
Operating Partnerships Total Expenses		1,214,946	1,260,765
NET LOSS		(188,454)	(193,294)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[11]	(186,569)	(191,361)
Net loss allocated to other Partners		(1,885)	(1,933)
Series Thirty [Member]
Revenues
Rental		751,561	1,234,713
Interest and other		45,948	24,356
Operating Partnerships Revenues		797,509	1,259,069
Expenses
Interest		91,581	137,653
Depreciation and amortization		202,659	262,136
Operating expenses		610,909	974,484
Operating Partnerships Total Expenses		905,149	1,374,273
NET LOSS		(107,640)	(115,204)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[12]	(106,564)	(114,052)
Net loss allocated to other Partners		(1,076)	(1,152)
Series Thirty One [Member]
Revenues
Rental		1,940,685	2,465,084
Interest and other		174,470	89,374
Operating Partnerships Revenues		2,115,155	2,554,458
Expenses
Interest		196,780	283,455
Depreciation and amortization		567,427	594,205
Operating expenses		1,541,743	1,901,611
Operating Partnerships Total Expenses		2,305,950	2,779,271
NET LOSS		(190,795)	(224,813)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[13]	(188,887)	(222,565)
Net loss allocated to other Partners		(1,908)	(2,248)
Series Thirty Two [Member]
Revenues
Rental		1,722,521	2,032,846
Interest and other		159,181	63,023
Operating Partnerships Revenues		1,881,702	2,095,869
Expenses
Interest		268,103	368,226
Depreciation and amortization		537,645	727,641
Operating expenses		1,427,978	1,391,384
Operating Partnerships Total Expenses		2,233,726	2,487,251
NET LOSS		(352,024)	(391,382)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[14]	(348,504)	(387,468)
Net loss allocated to other Partners		(3,520)	(3,914)
Series Thirty Three [Member]
Revenues
Rental		687,842	681,965
Interest and other		21,964	17,096
Operating Partnerships Revenues		709,806	699,061
Expenses
Interest		112,698	109,503
Depreciation and amortization		192,599	210,065
Operating expenses		518,800	452,542
Operating Partnerships Total Expenses		824,097	772,110
NET LOSS		(114,291)	(73,049)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[15]	(113,148)	(72,319)
Net loss allocated to other Partners		(1,143)	(730)
Series Thirty Four [Member]
Revenues
Rental		792,078	1,397,775
Interest and other		25,072	37,799
Operating Partnerships Revenues		817,150	1,435,574
Expenses
Interest		121,301	229,624
Depreciation and amortization		214,454	360,388
Operating expenses		618,888	944,799
Operating Partnerships Total Expenses		954,643	1,534,811
NET LOSS		(137,493)	(99,237)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[16]	(136,118)	(98,245)
Net loss allocated to other Partners		(1,375)	(992)
Series Thirty Five [Member]
Revenues
Rental		1,175,230	1,578,198
Interest and other		38,304	51,707
Operating Partnerships Revenues		1,213,534	1,629,905
Expenses
Interest		224,588	316,275
Depreciation and amortization		412,269	468,066
Operating expenses		732,303	935,527
Operating Partnerships Total Expenses		1,369,160	1,719,868
NET LOSS		(155,626)	(89,963)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[17]	(154,070)	(89,063)
Net loss allocated to other Partners		(1,556)	(900)
Series Thirty Six [Member]
Revenues
Rental		317,822	1,507,446
Interest and other		8,517	25,672
Operating Partnerships Revenues		326,339	1,533,118
Expenses
Interest		57,271	283,848
Depreciation and amortization		97,781	485,787
Operating expenses		243,903	1,023,950
Operating Partnerships Total Expenses		398,955	1,793,585
NET LOSS		(72,616)	(260,467)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[18]	(71,890)	(257,862)
Net loss allocated to other Partners		(726)	(2,605)
Series Thirty Seven [Member]
Revenues
Rental		1,452,093	1,982,200
Interest and other		58,318	37,642
Operating Partnerships Revenues		1,510,411	2,019,842
Expenses
Interest		306,076	369,232
Depreciation and amortization		459,576	567,481
Operating expenses		1,053,614	1,444,391
Operating Partnerships Total Expenses		1,819,266	2,381,104
NET LOSS		(308,855)	(361,262)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[19]	(305,766)	(357,649)
Net loss allocated to other Partners		(3,089)	(3,613)
Series Thirty Eight [Member]
Revenues
Rental		1,756,776	1,869,747
Interest and other		45,784	56,081
Operating Partnerships Revenues		1,802,560	1,925,828
Expenses
Interest		304,848	345,016
Depreciation and amortization		420,171	526,055
Operating expenses		1,187,985	1,314,846
Operating Partnerships Total Expenses		1,913,004	2,185,917
NET LOSS		(110,444)	(260,089)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[20]	(109,340)	(257,488)
Net loss allocated to other Partners		(1,104)	(2,601)
Series Thirty Nine [Member]
Revenues
Rental		746,462	1,358,384
Interest and other		28,669	60,845
Operating Partnerships Revenues		775,131	1,419,229
Expenses
Interest		148,585	246,902
Depreciation and amortization		172,026	386,912
Operating expenses		534,006	1,037,607
Operating Partnerships Total Expenses		854,617	1,671,421
NET LOSS		(79,486)	(252,192)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[21]	(78,691)	(249,670)
Net loss allocated to other Partners		(795)	(2,522)
Series Forty [Member]
Revenues
Rental		1,448,000	2,168,775
Interest and other		29,090	67,170
Operating Partnerships Revenues		1,477,090	2,235,945
Expenses
Interest		290,153	446,834
Depreciation and amortization		434,196	697,543
Operating expenses		1,003,602	1,374,402
Operating Partnerships Total Expenses		1,727,951	2,518,779
NET LOSS		(250,861)	(282,834)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[22]	(248,352)	(280,006)
Net loss allocated to other Partners		(2,509)	(2,828)
Series Forty One [Member]
Revenues
Rental		2,720,284	2,801,800
Interest and other		73,131	91,172
Operating Partnerships Revenues		2,793,415	2,892,972
Expenses
Interest		547,115	542,600
Depreciation and amortization		678,310	721,750
Operating expenses		1,828,142	1,739,882
Operating Partnerships Total Expenses		3,053,567	3,004,232
NET LOSS		(260,152)	(111,260)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[23]	(257,550)	(110,147)
Net loss allocated to other Partners		(2,602)	(1,113)
Series Forty Two [Member]
Revenues
Rental		1,799,442	2,419,424
Interest and other		129,594	120,967
Operating Partnerships Revenues		1,929,036	2,540,391
Expenses
Interest		380,976	502,601
Depreciation and amortization		558,935	709,510
Operating expenses		1,364,820	1,615,686
Operating Partnerships Total Expenses		2,304,731	2,827,797
NET LOSS		(375,695)	(287,406)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[24]	(371,938)	(284,532)
Net loss allocated to other Partners		(3,757)	(2,874)
Series Forty Three [Member]
Revenues
Rental		2,590,713	3,238,064
Interest and other		109,734	119,246
Operating Partnerships Revenues		2,700,447	3,357,310
Expenses
Interest		382,972	498,924
Depreciation and amortization		875,902	994,350
Operating expenses		1,963,968	1,915,389
Operating Partnerships Total Expenses		3,222,842	3,408,663
NET LOSS		(522,395)	(51,353)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[25]	(517,171)	(50,839)
Net loss allocated to other Partners		(5,224)	(514)
Series Forty Four [Member]
Revenues
Rental		2,977,712	2,963,278
Interest and other		77,859	78,935
Operating Partnerships Revenues		3,055,571	3,042,213
Expenses
Interest		722,083	767,046
Depreciation and amortization		727,408	770,821
Operating expenses		1,702,100	1,709,863
Operating Partnerships Total Expenses		3,151,591	3,247,730
NET LOSS		(96,020)	(205,517)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[26]	(95,060)	(203,462)
Net loss allocated to other Partners		(960)	(2,055)
Series Forty Five [Member]
Revenues
Rental		3,583,687	3,612,886
Interest and other		68,543	68,998
Operating Partnerships Revenues		3,652,230	3,681,884
Expenses
Interest		513,990	506,207
Depreciation and amortization		1,005,493	1,002,855
Operating expenses		2,559,633	2,473,948
Operating Partnerships Total Expenses		4,079,116	3,983,010
NET LOSS		(426,886)	(301,126)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[27]	(422,617)	(298,115)
Net loss allocated to other Partners		(4,269)	(3,011)
Series Forty Six [Member]
Revenues
Rental		2,856,476	2,855,230
Interest and other		70,079	43,805
Operating Partnerships Revenues		2,926,555	2,899,035
Expenses
Interest		626,574	603,405
Depreciation and amortization		686,230	744,484
Operating expenses		1,919,406	1,790,565
Operating Partnerships Total Expenses		3,232,210	3,138,454
NET LOSS		(305,655)	(239,419)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	[28]	(302,598)	(237,025)
Net loss allocated to other Partners		$ (3,057)	$ (2,394)

[1] Amounts include $(4,876,047) and $(4,406,179) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[2] Amounts include $(27,089) and $(21,196) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[3] Amounts include $(535) and $(23,614) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[4] Amounts include $(33,817) and $(41,918) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[5] Amounts include $(183,428) and $(154,991) for 2016 and 2015, of net loss not recognized under the equity method of accounting.

[6] Amounts include $(66,524) and $(88,658) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[7] Amounts include $(22,331) and $(17,185) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[8] Amounts include $(310,839) and $(253,390) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[9] Amounts include $(106,672) and $(12,033) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[10] Amounts include $(109,979) and $(194,111) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[11] Amounts include $(186,569) and $(191,361) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[12] Amounts include $(106,564) and $(114,052) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[13] Amounts include $(188,887) and $(222,565) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[14] Amounts include $(348,504) and $(387,468) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[15] Amounts include $(113,148) and $(72,319) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[16] Amounts include $(136,118) and $(98,245) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[17] Amounts include $(154,070) and $(89,063) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[18] Amounts include $(71,890) and $(257,862) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[19] Amounts include $(305,766) and $(357,649) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[20] Amounts include $(109,340) and $(257,488) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[21] Amounts include $(78,691) and $(249,670) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[22] Amounts include $(248,352) and $(280,006) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[23] Amounts include $(257,550) and $(110,147) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[24] Amounts include $(371,938) and $(284,532) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[25] Amounts include $(517,171) and $(50,839) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[26] Amounts include $(95,060) and $(203,462) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[27] Amounts include $(422,617) and $(259,106) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.

[28] Amounts include $(302,598) and $(113,249) for 2016 and 2015, respectively, of net loss not recognized under the equity method of accounting.