If I earn $60,000 a year or $30/hr during OPT , how much do I get after the taxes, in my hand ? How is Per Diem calculated ? And so how much do I get during H1b status ?

Thanks.

Assuming you are single, your federal income tax liability will be about $9,400.

Per diem rates are published by the IRS. You can access them at Internal Revenue Service (IRS Pub 1542).

When you switch to H-1B status, you become liable for Social Security and Medicare taxes. The flat tax rates ate 6.2% for SS and 1.45% for Medicare.