What is tax withholding?

Tax withholding is the portion of your paycheck your employer sends directly to the IRS on your behalf before you ever see it. The amount is based on your W-4 elections. If too much is withheld you get a refund; too little and you'll owe at filing.

Federal income tax is a pay-as-you-go system. Rather than paying a lump sum when you file in April, you pay throughout the year — primarily through withholding, where your employer deducts taxes from each paycheck and forwards them to the IRS. At year-end, you file a return to reconcile: if withholding exceeded your actual tax liability you get a refund; if it fell short you owe the balance.

How withholding amounts are determined

Your withholding is controlled by the W-4 form you submit to your employer. The redesigned W-4 uses your filing status, multiple-job adjustments, dependent credits, and other income/deductions to compute a withholding amount. Your employer runs that information through IRS Publication 15-T withholding tables to calculate the exact dollar amount to hold from each paycheck.

Withholding applies to wages, salaries, bonuses, and some other income types.
You can submit a new W-4 to your employer at any time to adjust your withholding.
Under-withholding can result in a tax penalty at filing time.
Self-employed individuals don't have withholding — they pay via quarterly estimated taxes instead.
FICA taxes (Social Security and Medicare) are also withheld separately from income tax withholding.

Under-withholding and penalties

If you pay less than 90% of the current year's tax liability (or less than 100% of last year's liability) through withholding and estimated payments combined, the IRS may assess an underpayment penalty. The IRS underpayment penalty page explains the thresholds and how to compute it. The IRS Tax Withholding Estimator is the recommended tool to check whether your current withholding is on track mid-year.

Withholding on non-wage income

Withholding also applies to certain non-wage income: pension and retirement distributions, gambling winnings, and some investment income. For income not subject to automatic withholding — such as self-employment earnings, rental income, or freelance payments — you're generally required to make quarterly estimated tax payments to stay current with the IRS.

IRS withholding facts

The U.S. federal income tax system is pay-as-you-go: taxpayers must pay most of their tax during the year as income is earned through withholding or estimated tax payments. — IRS
Employers use IRS Publication 15-T to determine the correct amount of federal income tax to withhold from employee wages. — IRS
The IRS Tax Withholding Estimator is a free online tool that helps employees determine whether their current withholding is appropriate. — IRS

Key takeaways

Withholding is income tax deducted from each paycheck and remitted to the IRS before you receive your pay.
Your W-4 form controls how much is withheld — update it any time your situation changes.
Too little withholding can trigger an IRS underpayment penalty at tax time.
Self-employed people have no withholding and must cover their tax bill through quarterly estimated payments.
Use the free IRS Tax Withholding Estimator mid-year to check whether you're on track.