As per the previous norms generally any candidate use to get rank upto 2.5 lac, it means that if someone is under 2.5 lac rank is eligible for JEE Advanced. So one can do simple calculation to compute that if someone is scoring more than 78 or 80 percentile will get a rank under 2.5 lac which will be safe percentile to appear in JEE Advanced. So, it will be great if your percentile is more than 80, then there is nothing to worry about. Even if your percentile is in bracket of +-5% then also there will be fair chance of gatting less than 2.5 lac rank. So, start preparing for JEE Advance as miracle happens at the last moment.

Best of luck.