INVESTMENTS IN OPERATING PARTNERSHIPS (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Revenues
Rental	$ 33,139,905		$ 35,357,571
Interest and other	946,955		1,051,584
Operating Partnerships Revenues	34,086,860		36,409,155
Expenses
Interest	6,389,626		7,297,759
Depreciation and amortization	9,851,546		10,463,735
Operating expenses	21,953,822		23,269,874
Operating Partnerships Total Expenses	38,194,994		41,031,368
NET LOSS	(4,108,134)		(4,622,213)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(4,067,049)	[1]	(4,575,990)	[1]
Net loss allocated to other Partners	(41,085)		(46,223)
Series Twenty [Member]
Revenues
Rental	661,277		671,891
Interest and other	9,074		18,476
Operating Partnerships Revenues	670,351		690,367
Expenses
Interest	124,387		105,536
Depreciation and amortization	162,247		171,357
Operating expenses	459,324		464,721
Operating Partnerships Total Expenses	745,958		741,614
NET LOSS	(75,607)		(51,247)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(74,851)	[2]	(50,735)	[2]
Net loss allocated to other Partners	(756)		(512)
Series Twenty One [Member]
Revenues
Rental	490,086		477,583
Interest and other	6,035		8,792
Operating Partnerships Revenues	496,121		486,375
Expenses
Interest	125,449		157,053
Depreciation and amortization	90,309		96,439
Operating expenses	296,220		301,588
Operating Partnerships Total Expenses	511,978		555,080
NET LOSS	(15,857)		(68,705)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(15,698)	[3]	(68,018)	[3]
Net loss allocated to other Partners	(159)		(687)
Series Twenty Two [Member]
Revenues
Rental	432,208		866,753
Interest and other	6,463		22,798
Operating Partnerships Revenues	438,671		889,551
Expenses
Interest	74,144		132,424
Depreciation and amortization	101,660		275,593
Operating expenses	324,028		556,283
Operating Partnerships Total Expenses	499,832		964,300
NET LOSS	(61,161)		(74,749)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(60,549)	[4]	(74,002)	[4]
Net loss allocated to other Partners	(612)		(747)
Series Twenty Three [Member]
Revenues
Rental	777,025		934,703
Interest and other	33,334		30,991
Operating Partnerships Revenues	810,359		965,694
Expenses
Interest	133,817		146,930
Depreciation and amortization	170,071		213,075
Operating expenses	516,424		675,396
Operating Partnerships Total Expenses	820,312		1,035,401
NET LOSS	(9,953)		(69,707)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(9,852)	[5]	(69,009)	[5]
Net loss allocated to other Partners	(101)		(698)
Series Twenty Four [Member]
Revenues
Rental	547,649		709,150
Interest and other	11,597		21,225
Operating Partnerships Revenues	559,246		730,375
Expenses
Interest	78,191		112,882
Depreciation and amortization	167,495		171,016
Operating expenses	373,268		499,660
Operating Partnerships Total Expenses	618,954		783,558
NET LOSS	(59,708)		(53,183)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(59,111)	[6]	(52,651)	[6]
Net loss allocated to other Partners	(597)		(532)
Series Twenty Five [Member]
Revenues
Rental	330,118		625,517
Interest and other	5,673		12,739
Operating Partnerships Revenues	335,791		638,256
Expenses
Interest	53,419		108,342
Depreciation and amortization	81,318		140,311
Operating expenses	273,747		415,535
Operating Partnerships Total Expenses	408,484		664,188
NET LOSS	(72,693)		(25,932)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(71,966)	[7]	(25,673)	[7]
Net loss allocated to other Partners	(727)		(259)
Series Twenty Six [Member]
Revenues
Rental	1,430,194		2,132,464
Interest and other	76,918		86,164
Operating Partnerships Revenues	1,507,112		2,218,628
Expenses
Interest	259,143		378,191
Depreciation and amortization	469,647		534,679
Operating expenses	1,067,822		1,562,236
Other expenses	1,796,612		2,475,106
NET LOSS	(289,500)		(256,478)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(286,605)	[8]	(253,913)	[8]
Net loss allocated to other Partners	(2,895)		(2,565)
Series Twenty Seven [Member]
Revenues
Rental	1,377,433		1,386,038
Interest and other	16,709		18,198
Operating Partnerships Revenues	1,394,142		1,404,236
Expenses
Interest	286,600		326,859
Depreciation and amortization	315,420		333,498
Operating expenses	813,078		784,124
Operating Partnerships Total Expenses	1,415,098		1,444,481
NET LOSS	(20,956)		(40,245)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(20,746)	[9]	(39,843)	[9]
Net loss allocated to other Partners	(210)		(402)
Series Twenty Eight [Member]
Revenues
Rental	1,711,027		1,840,175
Interest and other	23,901		40,229
Operating Partnerships Revenues	1,734,928		1,880,404
Expenses
Interest	293,430		325,514
Depreciation and amortization	476,903		501,463
Operating expenses	1,160,120		1,219,404
Operating Partnerships Total Expenses	1,930,453		2,046,381
NET LOSS	(195,525)		(165,977)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(193,570)	[10]	(164,317)	[10]
Net loss allocated to other Partners	(1,955)		(1,660)
Series Twenty Nine [Member]
Revenues
Rental	1,955,470		1,884,898
Interest and other	48,632		43,994
Operating Partnerships Revenues	2,004,102		1,928,892
Expenses
Interest	349,173		340,998
Depreciation and amortization	651,061		608,805
Operating expenses	1,326,824		1,170,900
Operating Partnerships Total Expenses	2,327,058		2,120,703
NET LOSS	(322,956)		(191,811)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(319,726)	[11]	(189,893)	[11]
Net loss allocated to other Partners	(3,230)		(1,918)
Series Thirty [Member]
Revenues
Rental	1,143,464		1,215,485
Interest and other	33,537		18,196
Operating Partnerships Revenues	1,177,001		1,233,681
Expenses
Interest	152,492		192,535
Depreciation and amortization	249,766		253,602
Operating expenses	896,097		977,077
Operating Partnerships Total Expenses	1,298,355		1,423,214
NET LOSS	(121,354)		(189,533)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(120,140)	[12]	(187,638)	[12]
Net loss allocated to other Partners	(1,214)		(1,895)
Series Thirty One [Member]
Revenues
Rental	2,453,810		2,695,740
Interest and other	72,987		90,806
Operating Partnerships Revenues	2,526,797		2,786,546
Expenses
Interest	380,237		477,701
Depreciation and amortization	716,682		785,072
Operating expenses	1,672,169		1,770,420
Operating Partnerships Total Expenses	2,769,088		3,033,193
NET LOSS	(242,291)		(246,647)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(239,868)	[13]	(244,181)	[13]
Net loss allocated to other Partners	(2,423)		(2,466)
Series Thirty Two [Member]
Revenues
Rental	1,458,766		1,465,835
Interest and other	54,936		47,751
Operating Partnerships Revenues	1,513,702		1,513,586
Expenses
Interest	294,133		310,091
Depreciation and amortization	544,169		516,648
Operating expenses	994,795		985,303
Operating Partnerships Total Expenses	1,833,097		1,812,042
NET LOSS	(319,395)		(298,456)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(316,201)	[14]	(295,471)	[14]
Net loss allocated to other Partners	(3,194)		(2,985)
Series Thirty Three [Member]
Revenues
Rental	661,949		672,850
Interest and other	22,297		24,043
Operating Partnerships Revenues	684,246		696,893
Expenses
Interest	144,239		171,320
Depreciation and amortization	229,802		224,779
Operating expenses	434,486		417,017
Operating Partnerships Total Expenses	808,527		813,116
NET LOSS	(124,281)		(116,223)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(123,038)	[15]	(115,061)	[15]
Net loss allocated to other Partners	(1,243)		(1,162)
Series Thirty Four [Member]
Revenues
Rental	1,445,327		1,529,406
Interest and other	41,334		49,985
Operating Partnerships Revenues	1,486,661		1,579,391
Expenses
Interest	216,240		300,404
Depreciation and amortization	476,764		578,645
Operating expenses	930,394		1,098,933
Operating Partnerships Total Expenses	1,623,398		1,977,982
NET LOSS	(136,737)		(398,591)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(135,370)	[16]	(394,605)	[16]
Net loss allocated to other Partners	(1,367)		(3,986)
Series Thirty Five [Member]
Revenues
Rental	1,091,046		1,227,675
Interest and other	40,215		37,865
Operating Partnerships Revenues	1,131,261		1,265,540
Expenses
Interest	203,764		258,974
Depreciation and amortization	370,326		416,954
Operating expenses	710,534		805,320
Operating Partnerships Total Expenses	1,284,624		1,481,248
NET LOSS	(153,363)		(215,708)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(151,829)	[17]	(213,551)	[17]
Net loss allocated to other Partners	(1,534)		(2,157)
Series Thirty Six [Member]
Revenues
Rental	739,281		898,899
Interest and other	18,769		17,038
Operating Partnerships Revenues	758,050		915,937
Expenses
Interest	140,851		216,108
Depreciation and amortization	226,886		235,574
Operating expenses	534,342		547,895
Operating Partnerships Total Expenses	902,079		999,577
NET LOSS	(144,029)		(83,640)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(142,589)	[18]	(82,804)	[18]
Net loss allocated to other Partners	(1,440)		(836)
Series Thirty Seven [Member]
Revenues
Rental	1,124,113		1,075,612
Interest and other	29,831		25,048
Operating Partnerships Revenues	1,153,944		1,100,660
Expenses
Interest	160,669		190,142
Depreciation and amortization	394,435		398,952
Operating expenses	862,315		879,734
Operating Partnerships Total Expenses	1,417,419		1,468,828
NET LOSS	(263,475)		(368,168)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(260,840)	[19]	(364,486)	[19]
Net loss allocated to other Partners	(2,635)		(3,682)
Series Thirty Eight [Member]
Revenues
Rental	904,723		884,576
Interest and other	16,637		28,785
Operating Partnerships Revenues	921,360		913,361
Expenses
Interest	181,654		194,411
Depreciation and amortization	242,647		258,984
Operating expenses	592,883		551,258
Operating Partnerships Total Expenses	1,017,184		1,004,653
NET LOSS	(95,824)		(91,292)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(94,866)	[20]	(90,379)	[20]
Net loss allocated to other Partners	(958)		(913)
Series Thirty Nine [Member]
Revenues
Rental	687,199		623,814
Interest and other	21,580		34,892
Operating Partnerships Revenues	708,779		658,706
Expenses
Interest	128,590		126,343
Depreciation and amortization	225,230		237,028
Operating expenses	491,348		479,214
Operating Partnerships Total Expenses	845,168		842,585
NET LOSS	(136,389)		(183,879)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(135,025)	[21]	(182,040)	[21]
Net loss allocated to other Partners	(1,364)		(1,839)
Series Forty [Member]
Revenues
Rental	1,023,872		1,223,024
Interest and other	26,354		26,656
Operating Partnerships Revenues	1,050,226		1,249,680
Expenses
Interest	242,209		236,331
Depreciation and amortization	329,794		335,702
Operating expenses	785,718		807,429
Operating Partnerships Total Expenses	1,357,721		1,379,462
NET LOSS	(307,495)		(129,782)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(304,420)	[22]	(128,484)	[22]
Net loss allocated to other Partners	(3,075)		(1,298)
Series Forty One [Member]
Revenues
Rental	1,388,428		1,387,523
Interest and other	35,370		36,868
Operating Partnerships Revenues	1,423,798		1,424,391
Expenses
Interest	290,163		306,433
Depreciation and amortization	563,850		554,592
Operating expenses	764,691		768,661
Operating Partnerships Total Expenses	1,618,704		1,629,686
NET LOSS	(194,906)		(205,295)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(192,957)	[23]	(203,242)	[23]
Net loss allocated to other Partners	(1,949)		(2,053)
Series Forty Two [Member]
Revenues
Rental	1,601,125		1,513,307
Interest and other	45,726		60,165
Operating Partnerships Revenues	1,646,851		1,573,472
Expenses
Interest	323,803		335,210
Depreciation and amortization	439,472		429,751
Operating expenses	936,930		897,403
Operating Partnerships Total Expenses	1,700,205		1,662,364
NET LOSS	(53,354)		(88,892)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(52,820)	[24]	(88,003)	[24]
Net loss allocated to other Partners	(534)		(889)
Series Forty Three [Member]
Revenues
Rental	1,870,431		1,822,149
Interest and other	60,738		48,761
Operating Partnerships Revenues	1,931,169		1,870,910
Expenses
Interest	354,931		358,145
Depreciation and amortization	542,379		571,057
Operating expenses	1,138,874		1,088,352
Operating Partnerships Total Expenses	2,036,184		2,017,554
NET LOSS	(105,015)		(146,644)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(103,965)	[25]	(145,178)	[25]
Net loss allocated to other Partners	(1,050)		(1,466)
Series Forty Four [Member]
Revenues
Rental	1,987,330		1,774,948
Interest and other	73,412		66,888
Operating Partnerships Revenues	2,060,742		1,841,836
Expenses
Interest	591,617		615,518
Depreciation and amortization	594,764		587,579
Operating expenses	1,073,797		1,064,700
Operating Partnerships Total Expenses	2,260,178		2,267,797
NET LOSS	(199,436)		(425,961)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(197,442)	[26]	(421,701)	[26]
Net loss allocated to other Partners	(1,994)		(4,260)
Series Forty Five [Member]
Revenues
Rental	2,475,615		2,472,015
Interest and other	70,198		86,233
Operating Partnerships Revenues	2,545,813		2,558,248
Expenses
Interest	496,552		562,129
Depreciation and amortization	710,450		700,739
Operating expenses	1,606,885		1,590,259
Operating Partnerships Total Expenses	2,813,887		2,853,127
NET LOSS	(268,074)		(294,879)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(265,393)	[27]	(291,930)	[27]
Net loss allocated to other Partners	(2,681)		(2,949)
Series Forty Six [Member]
Revenues
Rental	1,370,939		1,345,541
Interest and other	44,698		47,998
Operating Partnerships Revenues	1,415,637		1,393,539
Expenses
Interest	309,729		311,235
Depreciation and amortization	307,999		331,841
Operating expenses	916,709		891,052
Operating Partnerships Total Expenses	1,534,437		1,534,128
NET LOSS	(118,800)		(140,589)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.*	(117,612)		(139,182)
Net loss allocated to other Partners	$ (1,188)		$ (1,407)

[1] Amounts include $(3,574,669) and $(3,882,388) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[2] Amounts include $(74,851) and $(50,735) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[3] Amounts include $(15,698) and $(68,018) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[4] Amounts include $(60,549) and $(74,002) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[5] Amounts include $(9,852) and $(69,009) for 2013 and 2012, of net loss not recognized under the equity method of accounting.

[6] Amounts include $(59,111) and $(52,651) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[7] Amounts include $(71,966) and $(25,673) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[8] Amounts include $(286,605) and $(253,913) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[9] Amounts include $(20,746) and $(39,843) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[10] Amounts include $(193,570) and $(164,317) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[11] Amounts include $(319,726) and $(189,893) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[12] Amounts include $(120,140) and $(187,638) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[13] Amounts include $(239,868) and $(244,181) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[14] Amounts include $(316,201) and $(295,471) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[15] Amounts include $(123,038) and $(115,061) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[16] Amounts include $(135,370) and $(394,605) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[17] Amounts include $(151,829) and $(213,551) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[18] Amounts include $(142,589) and $(82,804) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[19] Amounts include $(260,840) and $(364,486) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[20] Amounts include $(94,866) and $(65,606) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[21] Amounts include $(135,025) and $(129,472) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[22] Amounts include $(304,420) and $(65,340) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[23] Amounts include $(192,957) and $(98,904) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[24] Amounts include $(9,900) and $(91,838) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[25] Amounts include $(7,958) and $(106,146) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[26] Amounts include $(168,794) and $(340,175) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.

[27] Amounts include $(58,200) and $(99,056) for 2013 and 2012, respectively, of net loss not recognized under the equity method of accounting.