Hello.

This minimum percentile game is tricky. There are things that you need to keep in mind:
1) which IIM are you looking at? - For IIM Ahmedabad your academic qualifications are not very important. A 65+ in each of X, XII and graduation (if grads>70m, then X or XII could be between 60 and 65 as well) will ensure that you clear the minimum academic rating score. Thus, all that matters is that you clear the cut-off (99.65+). Others like IIM B need you to have a decent academic background

2) Your academic background - Say you are one of those who has scored 90+ in X and XII and 80+ in graduation, then even a 96-97 percentile might fetch you a call from IIM B, K, I and the likes.

If your acads are okayish, then aim for a 98.5+ and you stand a chance to get a call from at least one of the IIMs.

Hope this is helpful.

Good luck.