How do I calculate how much to pay in Federal income tax last year?

To calculate your Federal income tax for last year, start by determining your total taxable income, which includes wages, interest, dividends, and any other income sources. Subtract any deductions you're eligible for, such as the standard deduction or itemized deductions, to arrive at your taxable income. Then, apply the appropriate tax brackets based on your filing status (single, married filing jointly, etc.) to calculate your tax liability. Finally, consider any credits or prepayments, such as withholding and estimated tax payments, to find out your final tax owed or refund amount.