Surajit, the official cutoff of JEE Mains will be released along with the final results once the April session is conducted. Then NTA will announce the category wise qualifying cutoff for JEE Advanced which will be displayed on the result portal.

Although you can check your expected rank using the formula:

(100-your total percentile) x 869010/100

So with 85 percentile, your rank would be around 130351.

Also, if the number of students increases to 12 lakh in the April session, the formula for rank calculation would change to:

(100-your total percentile) x 1200000/100

Hence your expected rank in this case would be around 180000.

Now the cutoff percentile is expected to change every year depending on the number of seats available and the number of students appearing. While it is difficult to predict the exact qualifying cutoff, a percentile of 85 or above is decent enough to qualify for JEE Advanced. You can also go through the previous years' cutoff to get an idea. In 2019, the NTA score cutoff for the Common Rank List was 89.7548849

According to your percentile, you have a decent chance to clear the cutoffs. Although I would suggest you to sit for the April session too and give your best in that exam so that your chance of qualifying JEE Mains and getting a top college increases. Solve the previous years' papers, brush up your concepts and revise thoroughly.

You can also go through our college predictor to check which colleges you are eligible for through your JEE Mains score. The link for the college predictor is:

All the best.