Formula and method
Annual estimated net pay equals wages minus traditional retirement deferrals, federal income tax, employee Social Security, Medicare and the entered allowances. Divide by pay periods. Traditional 401(k) deferrals reduce modeled income tax, but not Social Security and Medicare wages.
Worked example
At $200,000 annual employee wages, 2026 Social Security tax is capped at $184,500 × 6.2% = $11,439. Medicare at 1.45% is $2,900. A single filer reaches, but does not exceed, the $200,000 Additional Medicare threshold.