United States · Form W-4 · Federal income tax withholding

Over or under withholding check.

Use your latest pay stub to project whether your 2026 withholding will cover your tax, and how much extra to add per paycheck if it will not.

Add your withholding so far to the rest of the year at the current rate, then compare it with an estimate of your 2026 tax. The IRS general rule (Pub. 505) is to have withholding and credits of at least the smaller of 90% of 2026 tax or 100% of 2025 tax (110% if 2025 AGI was over $150,000), and no estimated tax is needed if you will owe under $1,000.

Tax year 2026IRS Pub. 505 (2026), Rev. Proc. 2025-32Retrieved October 2026

Your numbers

Filing status

Pay frequency

Paychecks received so far this year

Federal income tax withheld so far ($)From the year-to-date column on your latest pay stub.

Federal income tax withheld per paycheck now ($)

Expected wages for the whole year ($)Taxable wages for 2026 including what you have earned already.

Other income for the year ($)Interest, dividends, side income. Self-employment tax is not included here.

Adjustments to income ($)Student loan interest, IRA contributions, HSA and similar.

Itemized deductions, if more than the standard deduction ($)Leave at 0 to use the standard deduction ($32,200 joint, $24,150 head of household, $16,100 otherwise).

Tax credits ($)For example $2,200 per qualifying child under 17. Treated as reducing tax to no less than zero.

2025 total tax, optional ($)Form 1040 line 24 from your 2025 return, for the prior-year safe harbor.

2025 adjusted gross income, optional ($)Decides whether 100% or 110% of last year’s tax is used.

Projected refund or balance due

How the projection works

Projected withholding = withholding so far + (paychecks left × current withholding per paycheck). Estimated tax: income = wages + other income − adjustments, less the larger of the standard deduction or your itemized deductions, taxed with the 2026 brackets in IRS Rev. Proc. 2025-32 (Tables 1 to 4), minus credits and not below zero. Difference = projected withholding − estimated tax. A positive number is a refund; a negative one is a balance due.

If you would owe, the extra per paycheck is the shortfall divided by remaining paychecks, rounded up to the cent. Add it to your current Step 4(c) on a new Form W-4. A change made earlier in the year spreads the shortfall over more paychecks.

Worked example

Single, paid every two weeks, 13 paychecks received, $2,000 withheld so far, $150 per paycheck now, $60,000 of wages. Taxable income = $60,000 − $16,100 = $43,900. Tax = $1,240 + 12% × ($43,900 − $12,400) = $5,020. Projected withholding = $2,000 + 13 × $150 = $3,950. Shortfall = $1,070, or $82.31 more on each of the 13 remaining paychecks. 90% of the tax is $4,518, so the 90% safe harbor is also missed.

Safe harbor and penalties

Pub. 505 says you generally must pay estimated tax if you expect to owe at least $1,000 after withholding and credits and your withholding and credits will be less than the smaller of 90% of your 2026 tax or 100% of your 2025 tax (110% if your 2025 AGI was over $150,000, or $75,000 if married filing separately). The 2025 return must cover 12 months. The page tests both against your projected withholding, but whether a penalty applies depends on timing of payments too; see the underpayment penalty calculator.

Not modelled

Self-employment tax, the Additional Medicare Tax, the Net Investment Income Tax, the alternative minimum tax, capital gains rates, refundable credits, phase-outs, state tax and bonuses paid later in the year. Use the IRS Tax Withholding Estimator when any of those apply.

Sources

IRS Publication 505 (2026), Chapter 2 and Figure 2-A: who must pay estimated tax, the 90% / 100% / 110% rule and the $1,000 threshold.
IRS Rev. Proc. 2025-32 sections 4.01 and 4.14: 2026 tax rate tables and standard deduction amounts.
IRS Form W-4 (2026): Step 4(c) extra withholding per pay period.
All figures are for tax year 2026 and were retrieved from the IRS in October 2026. The IRS republishes them every year; this page covers 2026 only.

Frequently asked questions

How do I know if I am withholding too little?

Compare your projected full-year withholding with your estimated 2026 tax. If withholding is lower, you will owe the difference when you file. This page does that arithmetic from your year-to-date pay stub numbers.

How much extra should I add to Step 4(c)?

The shortfall divided by the number of paychecks left this year. Add it to whatever is already in Step 4(c) and give your employer a new Form W-4.

What is the safe harbor to avoid an underpayment penalty?

Per Publication 505, withholding and credits of at least the smaller of 90% of your 2026 tax or 100% of your 2025 tax (110% if your 2025 AGI was over $150,000), or owing less than $1,000 after withholding and credits.

Does this include Social Security and Medicare?

No. It only compares federal income tax withheld with federal income tax owed. FICA is a separate payroll tax and is not part of your Form 1040 income tax.

Estimate only

This page is educational and is not tax advice. It runs in your browser, stores nothing and does not check anything with the IRS or your employer. Your employer’s payroll system, your exact Form W-4 and your actual return decide what is really withheld and owed. For the most accurate result use the IRS Tax Withholding Estimator.