Hi. I am currently a student (on F-1 visa) and am planning to start my OPT. I wanted to know that what is the percentage of tax on my pay when I am on my OPT. Like we have to pay around 30% of our pay if we are on H-1.

Not so much on your status but very much on how much you will be making. If you are on the 30% tax bracket, then congrads, you are making a lot of money.