HELLO VIDYA
Firstly you need to qualify MAIns in order to write advance. WEll if you are aiming for IIT then getting a 99.6+ percentile in mains might be not a tough job for you by doing this all the top 5 NITS with cse branch are in your hand.
Now coming to IIT it depends which IIT you want to go into straight answer is your rank should be less than 8000 to get a IIT since nearly 11000 students qualify JEE ADVANCED.
Well for a detailed cut off list you can visit this link
https://engineering.careers360.com/articles/jee-advanced-cutoff
HOPE IT HELPS!!