Income-tax withholding follows payroll instructions
For supported ordinary wages with a 2020-or-later W-4, our federal engine uses the IRS Publication 15-T percentage method. It annualizes the period’s taxable wages, applies W-4 adjustments and the selected table, then converts the amount back to the pay period.
Filing status, the multiple-jobs checkbox, annual credits, other income, deductions and extra per-check withholding can change the result. A single percentage applied to every employee’s gross wages does not reproduce that method.
A pay-frequency example
Consider $2,000 taxable wages paid biweekly. The annualized wage amount starts at $2,000 × 26 = $52,000 before the method’s W-4 adjustments. The calculation then uses the appropriate withholding schedule. This is not the same as saying the employee’s final tax return must report exactly $52,000.
An extra $25 entered as per-paycheck withholding adds $25 to each supported paycheck calculation. By contrast, an annual credit is allocated across pay periods; it is not subtracted in full from every check.
Payroll taxes have their own calculation bases
Social Security and Medicare are separate from federal income-tax withholding. Social Security has an annual wage cap; ordinary Medicare does not. Employer Additional Medicare withholding uses employer-paid wages crossing $200,000, regardless of the employee’s filing status.
Enter prior year-to-date taxable wages when estimating a later paycheck. A check near a wage limit may differ from the first check of the year, so multiplying one check by 26 is not always a reliable annual net estimate.
State, local and annual-return differences
States use their own withholding certificates, formulas and benefit rules. Local taxes or employee contributions can add further deductions. Our state directory links only the engines that support the scenarios documented on their pages.
Your final annual liability considers the complete return and may differ from withholding. When deciding what to put on an actual W-4, review the official IRS estimator and your complete income situation rather than relying only on a single sample paycheck.
Frequently asked questions
Is a refund proof that withholding was calculated incorrectly?
No. Withholding and final liability can differ because the tax return includes credits, deductions, other income and payments that one paycheck cannot capture.
Does checking “exempt” remove every payroll tax?
No. A valid federal income-tax withholding exemption does not automatically remove Social Security or Medicare withholding. Eligibility and other withholding rules must still be checked.
Why do two people with the same salary receive different checks?
Different W-4 elections, benefit deductions, state or local circumstances and year-to-date wages can change the amount withheld.
Official references
- IRS Publication 15-T — withholding methods
- IRS Topic 751 — Social Security and Medicare
- IRS Tax Withholding Estimator
Educational examples explain the arithmetic and terminology. Check your actual pay records and the relevant rules for your situation.