Hi Chirag,

You haven't mentioned the name of exam you are referring to.

Seeing that you are an engineering aspirant, I am giving you info for JEE Main Examination.

As per the previous year marks percentile scores, you are required to get approximately 179+ marks to get 99.5+ percentile in 2020.

Refer here for more info - https://engineering.careers360.com/articles/jee-main-marks-vs-percentile#Details-of-JEE-Main-Percentile-vs-Marks

Feel free to ask doubts in the Comment Section.

I hope this information helps you.

Good Luck!