Yes, you can join NIFT after the 12th but there is some eligibility criterion that needs to be taken care of.
For B.Des. Course: You must pass your 12th from a recognized institute in any stream. Whereas, For B.F.Tech. Course: You must pass your 12th from a recognized institute with Mathematics, Physics & Chemistry as subjects. If you fulfill the above ones, you definitely can join NIFT after the 12th.
Good Luck!
