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Withholding is tax your employer takes from each paycheck for the IRS. Too little and you owe in April; too much and you lend the government your money.
First: run the IRS Tax Withholding Estimator with a recent pay stub in hand, then give your employer an updated W-4. The average 2026 refund as of May 8 was $3,276 (IRS), money you could have used all year.
Watch for: a second job, a marriage, a baby, or a bill or big refund last April. Change your W-4 as soon as one happens. Employers must apply it within about 30 days.
The W-4 goes to your employer, not the IRS, and you can change it any time. With two jobs, each employer withholds as though its paycheck is your only income — which is why two jobs can produce a bill in April.
Source: IRS Form W-4 and the IRS Tax Withholding Estimator.
What withholding actually is
Withholding is the share of each paycheck your employer sends to the IRS on your behalf. Set it too low and you owe in April. Set it too high and you get a refund.
A refund feels like a win and is really your own money coming back, without interest, after a year away. See Section 17 for the rest of the deductions on your stub.
What getting it wrong costs
Too little withheld: you owe the balance in April. You can also owe an underpayment penalty, based on how much you were short and for how long. There is no penalty if you owe less than $1,000, or if you paid at least 90% of this year's tax or 100% of last year's (110% if last year's adjusted gross income was over $150,000), whichever is less (IRS underpayment penalty page). Interest is 7% a year for the fourth quarter of 2026 (IRS).
Too much withheld: the average refund in the 2026 filing season, as of May 8, was $3,276 (IRS filing season statistics, May 8, 2026). That is money missing from your paychecks all year, earning nothing, that could have paid down a card or built an emergency fund.
Fixing it costs nothing. You can generally change your W-4 whenever you wish (IRS Publication 505).
The form, and who it goes to
The W-4 controls it. It goes to your employer or your payroll system, not to the IRS.
There is nothing to mail and no approval to wait for. Your employer has to apply the new form by the first payroll period ending on or after the 30th day after you hand it in (IRS Topic 753), and many do it sooner. Check your next paychecks and confirm the number moved; if it has not by day 30, ask payroll.
The moments worth revisiting it
You got married or divorced. You had a child — see Section 47. You took a second job, or your household went from one income to two. You started earning money with no tax withheld. You owed, or got a large refund, last April.
Two jobs is the one that catches people
Each employer withholds as though its paycheck is your only income. So both withhold at a low-income rate while your actual total sits in a higher bracket. Neither employer did anything wrong and you still owe in April.
The W-4 has a multiple-jobs step for exactly this. Skipping it can leave too little tax withheld (IRS Publication 505) — see Section 49.
If nothing is withheld at all
Self-employed, freelance or gig income has no withholding behind it. Quarterly estimated payments are the version of this that applies to you. See Section 20.
What you can do, in order
- Run the IRS Tax Withholding Estimator with a recent pay stub in hand.
- Give the new W-4 to your employer, or update it in your payroll system.
- Check your next paychecks after the change and confirm the number moved; if it has not by the first payroll period that ends on or after 30 days from when you turned the form in (IRS Topic 753), ask payroll.
- Working two jobs: do the multiple-jobs step. Skipping it is a common cause of an April bill.
- No withholding at all: set up quarterly estimated payments instead.
- Look at last year's return. If you owed $1,000 or more, consider fixing your withholding now, because you may owe an underpayment penalty (IRS Topic 306). If you got a big refund, lower it.
Where to check this yourself
irs.gov for the W-4, the Tax Withholding Estimator and quarterly estimated payments.