Yes,If you are a student of cbse board you must have at least 75% marks in 12 ^th board for Getting into NIT or IIT,but if you are a state board pass out student you must be within top 20 percentile for your board .

For some boards 20%ile may be less than 75%.

In case it is more than 75% u must at least get. 75% aggregate.

Gone are those days when Boards' Percentile used to be calculated and a normalized scored used to be generated based on 60% weightage to JEE Main Score & 40% weightage to Boards’ Percentile.

So, keep calm & study for JEE Main. Getting 65%/75% in Class 12th Board Exam is a cakewalk if you prepare well for JEE.

All The Best.

Hey,
Candidates should have obtained a minimum of 75% marks in class 12 or equivalent exam or they must be in the top 20 percentile in their class 12 examination. For SC/ ST, the eligibility is to obtain a minimum of 65% marks in class 12 or equivalent for NITs/IITs/GFTIs admissions.
For detailed information follow the link below:
https://engineering.careers360.com/articles/jee-main-eligibility-criteria
Hope this helps.
Good luck.

Yes, minimum 75% marks are compulsory to get into NIT or IIT if you belong to General/OBC and 65 % if you are from SC/ST category or you need to be in the top 20 percentile which is definitely more then 50% so you will not able to get admission into NIT or IIT.