How it works
The calculator works out your 2026 federal income tax from your wages, the standard deduction and the child tax credit, then adds up what your paychecks will have withheld by December 31: what's come out so far, plus this paycheck's amount for each one left. If that falls short, it spreads the gap over the paychecks you have left. That's the amount to enter as extra withholding in Step 4(c) of a new Form W-4, the same method IRS Publication 505 uses.
Extra per paycheck = (2026 tax − withheld so far − per-paycheck tax × paychecks left) ÷ paychecks left
Worked example
A single employee earns $65,000 a year, paid every two weeks. In late September their pay stub shows $3,600 of federal tax withheld so far and $200 this paycheck, with 7 paychecks to go. By December 31 that's $5,000.
After the $16,100 standard deduction their 2026 tax is $5,620, so they'd owe $620 in April. Adding $89 a paycheck in Step 4(c) closes the gap.
A married couple earning $180,000 with $20,000 of side income and two children owes $21,940 after the $4,400 child tax credit. Their withholding will reach only $18,750, leaving them $3,190 short. Last year's tax was $20,000 on an AGI over $150,000, so 110% of it is $22,000; 90% of this year's, $19,746, is smaller and is the bar to clear. $143 more a paycheck avoids the penalty, and $456 more means owing nothing.
Filling in the W-4
- Step 4(c), extra withholding. The dollar amount per paycheck on top of what your employer already takes. It's the simplest fix when you're short.
- Step 4(b), deductions. Lowers your withholding for deductions beyond the standard one, including the new ones for tips, overtime, car loan interest and seniors. Use it when you're over-withholding.
- Step 2, more than one job. Two jobs, or two working spouses, are the most common reason for owing. The W-4's worksheet or the checkbox handles it.
- A big bonus. Bonuses are usually withheld at a flat 22%, which can fall short in a higher bracket. The bonus tax calculator shows the gap.
- When it takes effect. Your employer has until the first payroll period ending on or after the 30th day after you hand it in, and many change it sooner. Count only the paychecks left after that.
- Reset it in January. A Step 4(c) amount stays until you change it. If it was a catch-up for this year, hand in a new W-4 for 2027 or you'll over-withhold next year.
Avoiding the underpayment penalty
Owing at tax time isn't a problem in itself; owing too much can bring a penalty. You're generally safe if you owe less than $1,000 after withholding and refundable credits, or if your withholding covers the smaller of 90% of this year's tax and 100% of last year's. That last figure becomes 110% if last year's AGI was over $150,000.
Withholding has one advantage over estimated tax payments: the IRS counts it as paid in equal parts through the year, whenever it came out of your pay. Raising it in the fall still covers the earlier quarters.
The new deductions for tips, overtime, car loans and seniors
For 2025 to 2028 you can deduct qualified tips (up to $25,000) and the extra half of time-and-a-half overtime pay (up to $12,500, or $25,000 married filing jointly), both for incomes under $150,000 ($300,000 joint). You can also deduct interest on a loan for a new car assembled in the U.S. (up to $10,000, for incomes under $100,000 or $200,000 joint), plus $6,000 for each taxpayer 65 or older with income under $75,000 ($150,000 joint). Above those incomes the deductions shrink. You take them on top of the standard deduction, and the W-4's Step 4(b) worksheet has a line for each. Enter your total in the extra deductions field.
Things to know
- This is an estimate, not tax advice. It covers federal income tax only. It leaves out self-employment tax, itemized deductions and credits other than the child tax credit, such as the earned income credit.
- Side income with no withholding raises your tax too. Cover it here with extra withholding, or with quarterly payments: the estimated tax calculator works those out. If it's a business, the self-employment tax calculator breaks down the tax on it.
- For the full-year picture of brackets, credits and refund, use the income tax calculator. To see what a W-4 change does to your take-home pay, the paycheck calculator.
- 2027. The IRS usually publishes next year's brackets in October or November. We'll add the 2027 figures once it does.
Questions people ask
How much extra should I withhold per paycheck?
Take what you'd owe at year end, divide by the paychecks you have left, and round up. Enter that in Step 4(c) of a new Form W-4 and give it to your employer.
Why do I owe when tax comes out of every paycheck?
Usually because of a second job or a working spouse, since each employer withholds as if that job were your only income. Other common reasons are side income with no withholding, or a W-4 that no longer matches your life, for example after a child turns 17.
Is a big refund a good thing?
It means you lent the government money at 0% all year. A smaller refund means more in each paycheck, which could sit in a savings account earning interest instead.
Do I need a new W-4 every year?
No. Your W-4 stays in effect until you change it, unless you claimed exemption from withholding, which has to be renewed each year. Review it after a raise, a new job, marriage, or a new child.
Sources
- IRS: Form W-4 (2026), Employee’s Withholding Certificate
- IRS: Publication 505, Tax Withholding and Estimated Tax (2026)
- IRS: Rev. Proc. 2025-32 (2026 tax rate tables, standard deduction, child tax credit)
- IRS: Topic 306, penalty for underpayment of estimated tax
- IRS: Instructions for Form 2210 (withholding counted in equal parts)
- IRS: One, Big, Beautiful Bill provisions (tips, overtime, car loan interest, seniors)
Reviewed September 29, 2026 by The Dollars World team. How we build and check our calculators · Our data and formulas. This is general information, not financial advice.