Step 1: annualize
Multiply taxable wages for the period by the number of pay periods: 26 for biweekly, for example.
Step 2: subtract the standard deduction
Use the amount for the filing status on the W-4, plus any deductions the employee claimed.
Step 3: apply the brackets
2026 single brackets: 10% to $12,400, 12% to $50,400, 22% to $105,700, 24% to $201,775, 32% to $256,225, 35% to $640,600, then 37%.
Step 4: divide and adjust
Divide the annual tax by the number of pay periods, subtract credits for dependents and add any extra withholding the employee asked for.