Based on this article source, Several groups have expire their contract in 2016(* The exact duration of the contract idol group not publicly known. However, at present, the average and maximum contract term of idol group, should be considering 7 years)f(x), Beast, and 4minuteKara, Secret, and MBLAQ2NE1, T-ara, and Rainbow newsway via hannybee at onehallyuthe article isnt fully translated but you can get the gist anyway