How is tax calculated on lottery winnings?

How much you pay ultimately depends on your own tax situation and tax rate. There is no specific rate or category for income from types of gambling.

The withholding (like from a payroll, as an estimate of the tax) required at the casino is normally a minimum of 20%, but can depend again on your situation too. It is NOT the amount you pay...just a payment in advance to assure the amount you owe is paid.

Lottery and Gambling winnings are taxed like any other income.

That amount, or percent, of course changes with everyones personal situation, other income, expenses, deductions, exemptions, STATE (and state income tax is a deduction to Federal taxable income, so that changes many things), dependents, etc.

It is fair to say that 2 people, winning the same lottery would normally pay different amount of taxes.

Proveable losses are deductible against winning, so keep those losing lottery tickets!

Many people have tried to claim the winnings as Capital in nature, for the lower tax rate. The courts have denied that in each case.

If you are a professional gambler, the tax handling may change, as it is income from self employment...there are both good and bad aspects to this.