Hello,

The closing rank of NIT and IIITs vary a lot and depend on a lot of various factors like demand, infrastructure, branch, location, etc. So, it would be better if you can also tell which particular institute you want to know about. There are 31 NITs and around a dozen of good IIITs, thus mentioning closing and opening ranks of every NIT/IIIT is not practical. I would still give you a rough idea that seats get filled in NIT for other states before closing rank reaches 50k for general, 20k for OBC, 10k for SC and ST. Same goes for the good IIITs also. 

I am also attaching links for the cutoffs of NITs and IIITs for your convenience:

https://engineering.careers360.com/articles/jee-main-cutoff 

https://engineering.careers360.com/articles/jee-main-cutoff-for-top-iiits

Thank You