what is the percentile to get seat at nit?

Hello.
You didn't mention that in which NIT and in which branch you want to have admission for the same you should mention the name so that I could tell you the percentile required for that, still I am providing you a link below where you can see previous year cutoff list for all NIT which may help you to you know no the rank which need to maintain.
Link is given below:
https://engineering.careers360.com/articles/jee-main-cutoff
after knowing the cutoff of NITs you can use hit and trial method and using the below formula you can find out the percentile which is required to have a particular NIT:
Formula is given below:
Your approximate rank= ((100-your total percentile score) X total number of candidates appeared for the exam)/100
Total number of candidates appeared for the January exam: 869010
Let's suppose Total number of candidates for April exam increase to 12,00000
Now you have all values and you need to find your percentile score you can simply put the cut off rank on the place of your approximate rank  by using the above formula you can calculate your percentile score and remember the percentile score will be the approximate percentile score .
Best of luck.