Federal withholding is the money your employer pulls out of each paycheck and sends to the IRS on your behalf, so you pay your tax bill gradually across the year instead of all at once in April. Three separate taxes come out: federal income tax, Social Security tax, and Medicare tax. The income tax portion depends on what you put on your Form W-4. The Social Security and Medicare portions follow fixed rates written into law.
The Three Taxes That Come Out of Your Check
Every paycheck stub shows these lines separately because they work differently.
Federal Income Tax
This is the piece most people mean when they say “withholding.” Your employer calculates it using the filing status, dependents, and adjustments you reported on IRS Form W-4, plus how much you earned that pay period. Federal law requires every employer paying wages to deduct income tax according to IRS-prescribed tables or formulas.1Office of the Law Revision Counsel. 26 USC 3402 – Income Tax Collected at Source The federal income tax is progressive, so different slices of your annual income are taxed at increasing rates, and the tables your payroll department uses are built around those brackets.
Social Security and Medicare (FICA)
On top of income tax, your employer withholds Social Security tax at 6.2% of your wages and Medicare tax at 1.45%.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates Your employer pays a matching amount out of its own pocket. These rates are set by statute, and your W-4 does not affect them.3Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax
Social Security tax stops once your year-to-date wages cross an annual ceiling. For 2026, that cap is $184,500.4Social Security Administration. Maximum Taxable Earnings After you hit it, your employer stops withholding the 6.2% for the rest of the year. Medicare has no cap; the 1.45% applies to every dollar you earn.
Additional Medicare Tax for High Earners
If you earn more than $200,000 in a calendar year, your employer must withhold an extra 0.9% Medicare tax on wages above that threshold.5Internal Revenue Service. Questions and Answers for the Additional Medicare Tax Your employer applies the $200,000 trigger no matter your filing status. Married joint filers actually don’t owe the extra tax until combined wages hit $250,000, so any mismatch gets reconciled when you file your return.3Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax
How the Income Tax Portion Is Calculated
Your employer’s payroll system runs your W-4 information through IRS-published wage bracket tables or a percentage formula. Form W-4 asks for your filing status (single, married filing jointly, married filing separately, or head of household), any qualifying children under 17 or other dependents, and any adjustments for outside income or expected deductions.6Internal Revenue Service. Topic No. 753, Form W-4, Employees Withholding Certificate The tables also account for how often you’re paid, so the same annual salary produces different per-check withholding depending on whether you’re paid weekly, biweekly, semimonthly, or monthly.
New hires complete a W-4 during onboarding, but you can submit an updated one to payroll at any time. If you never file one, your employer isn’t allowed to simply skip withholding. Federal rules require them to treat you as a single filer with no dependents and no adjustments, which usually pulls more tax from each check than necessary.6Internal Revenue Service. Topic No. 753, Form W-4, Employees Withholding Certificate
One point worth clearing up: moving into a higher tax bracket does not mean all your income is taxed at the higher rate. Only the income sitting inside each bracket is taxed at that bracket’s rate. The withholding tables reflect that layered math automatically.
Why Paychecks From the Same Salary Don’t Always Match
Even if your annual salary is steady, the amount withheld from any given paycheck can swing. Temporary income bumps are the biggest reason. If you work overtime one week or get a commission check, the payroll system looks at that inflated check and withholds as though you earn that much every pay period. The result is heavier withholding on that particular check, even though your overall annual income hasn’t shifted much. It evens out on your return.
Bonuses and Supplemental Pay
Bonuses, commissions, and other supplemental wages have their own rules. Your employer can combine them with your regular wages and run the standard calculation, or use a flat-rate method. Supplemental wages up to $1 million in a calendar year are withheld at a flat 22%. Anything above $1 million in supplemental wages is withheld at 37%.7Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide That flat 22% is why a $5,000 bonus often looks smaller than you expect on payday. It has nothing to do with your actual tax bracket, and any over-withholding comes back when you file.
Changing Your Withholding
To adjust what your employer takes out, submit a new Form W-4 to payroll or HR. Once received, the employer must implement the update no later than the start of the first payroll period ending on or after the 30th day from receipt.6Internal Revenue Service. Topic No. 753, Form W-4, Employees Withholding Certificate
The IRS Tax Withholding Estimator at irs.gov is the practical way to check whether your current setup is on track. You enter your expected income, filing status, credits, and current withholding, and it tells you whether you’re heading toward a refund, a balance due, or roughly even. It can even generate a filled-in W-4 to print and hand to payroll.8Internal Revenue Service. Tax Withholding Estimator The IRS suggests checking at the start of each year and after major life changes such as marriage, a new child, or starting a side job.
Claiming Exempt
If you had no tax liability last year and expect none this year, you can write “exempt” on your W-4 and stop income tax withholding entirely. The exemption expires at year-end. To continue it, you must file a new W-4 claiming exempt by February 15 of the following year.6Internal Revenue Service. Topic No. 753, Form W-4, Employees Withholding Certificate Claiming exempt when you actually owe tax leads to a surprise bill and penalties in April, so this really only fits people with very low income or enough credits to zero out their liability.
How Withholding Reconciles at Tax Time
Everything withheld during the year appears on the W-2 your employer must provide by February 1 of the following year.9Internal Revenue Service. General Instructions for Forms W-2 and W-3 (2026) When you file your Form 1040, the IRS compares your total withholding (plus any estimated payments) against the tax you actually owe based on your return. Overpaid means a refund. Underpaid means you write a check. For most people the return is due April 15.10Internal Revenue Service. When to File
A large refund feels like a windfall, but it means you gave the government an interest-free loan across the year. Aiming for zero is risky in the other direction, because a small miscalculation can trigger an underpayment penalty. Most people target a modest refund or a small balance due.
Staying Out of Underpayment Penalty Territory
If your withholding falls too far short of what you owe, the IRS charges a penalty that behaves like interest on the shortfall. For 2026, that rate is 7% annually, calculated daily for each quarter you were underpaid.11Internal Revenue Service. Quarterly Interest Rates
You avoid the penalty if you meet any one of these safe harbors:12Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
- You owe less than $1,000 after subtracting withholding and credits.
- Your withholding and estimated payments covered at least 90% of the tax on your current-year return.
- Your withholding and estimated payments equaled at least 100% of the tax shown on last year’s return (which must cover a full 12 months).
Higher earners face a stricter version of that third rule. If your adjusted gross income last year exceeded $150,000 ($75,000 if married filing separately), the prior-year safe harbor rises to 110% of last year’s tax.12Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax Those thresholds are written into the statute and don’t adjust for inflation. If your income fluctuates a lot, the prior-year method is usually the safer bet because you already know the number.
When Withholding Alone Won’t Cover You
Federal withholding only applies to wages. Income from self-employment, freelancing, rental property, or investments doesn’t come with an employer taking taxes out. The IRS expects you to make quarterly estimated tax payments using Form 1040-ES. For the 2026 tax year, the deadlines are April 15, 2026; June 15, 2026; September 15, 2026; and January 15, 2027. You can skip the January payment if you file your 2026 return and pay the full balance by February 1, 2027.13Internal Revenue Service. 2026 Form 1040-ES, Estimated Tax for Individuals
The same safe harbor rules apply to estimated payments. If you have both a regular job and meaningful side income, a common workaround is to raise your W-4 withholding at work enough to cover the tax on the outside income. That spreads the payments across the year and avoids the quarterly paperwork.