There is one national level entrance i.e. NIMCET through which you can get admission in NITs in MCA program so if you wish apply for the same then the Application window opens in the month of Feb-March and exam held on last week of May.

Apart from this, there are various exams at state and university level and all have their own eligibility and admission process so please be specific if there is any particular one which you are aiming for.

And to know all about NIMCET 2018, you can go through the below link -

https://it.careers360.com/articles/nimcet

https://it.careers360.com/articles/nimcet-eligibility-criteria

Good Luck!!!