Hello, hope you are doing well, the answer to your question cannot be told in terms of percentage of marks but it is generally in terms of ranks. Like if you want top IIT's your rank should be very low (59-666). The mentioned rank is for the stream of cse. If you want to join any other stream also you need to get below 1000 rank to get admitted in top IIT's.

I think it is helpful!!!

Keep Smiling:)

Wish you good luck!:)