Assuming you are asking for NIMCET as this is the only national or common entrance for MCA then the exam held in the month of May but till now there is no particular date out for 2019-20 session.

Also, for 2018 the exam will take place on 27th May.

For reference, you can go through the below link -

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

Good Luck!!!