Tax Withholding: How to Make Sure You’re Not Overpaying (or Underpaying)

Published June 30, 2026 · 8 min read

Getting a $3,000 tax refund feels like a windfall — but it isn’t. It means you overpaid your taxes by $250 a month all year and let the IRS hold that money interest-free. On the flip side, owing $2,500 at tax time stings, and if you underpay significantly, the IRS charges you a penalty on top of the bill.

The good news: tax withholding is completely adjustable. You control it through your W-4 form. Here’s how to diagnose whether your withholding is off, understand why it happens, and fix it so you keep more money in your paycheck every month rather than waiting for a refund.

How Tax Withholding Works

When you start a job, you fill out a W-4 form that tells your employer how much federal income tax to withhold from each paycheck. Your employer uses that information along with IRS Publication 15 withholding tables to calculate the exact dollar amount to hold back every pay period.

Those withheld amounts go straight to the IRS on your behalf. When you file your tax return each spring, the IRS calculates your actual tax liability for the year. If you withheld too much, you get a refund. If you withheld too little, you owe the difference — and potentially a penalty. (IRS — Publication 505: Tax Withholding and Estimated Tax)

This means your W-4 is not a “set it and forget it” form. Every major life change — a new job, a marriage, a baby, buying a house, starting a side business — can shift your actual tax liability and leave your withholding misaligned.

Over-Withholding: Why a Big Refund Is Actually a Problem

Over-withholding is by far the more common problem. According to IRS data, the majority of US taxpayers receive a refund each year — with the average refund hovering around $3,000. (IRS — Filing Season Statistics)

A $3,000 refund sounds great, but here’s the math: that’s $250 per month that could have stayed in your paycheck, been invested, or been used to pay down debt. The IRS pays zero interest on refunds (except in rare cases when it issues them late), so you’re essentially giving the government a $3,000 interest-free loan for up to 16 months.

Common reasons people over-withhold:

• Haven’t updated a W-4 in years. The IRS redesigned the W-4 in 2020 and old forms may result in higher withholding than needed.
• Got married. Married filing jointly has a larger standard deduction ($30,000 in 2026) and lower combined tax bills, but both spouses’ W-4s may not reflect the new status.
• Had a child. Claiming the Child Tax Credit (up to $2,000 per child) significantly reduces what you owe, but only if your W-4 reflects those credits.
• Bought a home. Mortgage interest deductions can substantially lower taxable income if you itemize.
• Requested extra withholding. Some people add extra withholding to avoid a surprise bill — and forget to remove it when their situation changes.

Under-Withholding: When You Owe Money (and Get Penalized)

Under-withholding is less common but more painful. It means you owe the IRS money at filing time — and if you under-withheld significantly, you also owe an underpayment penalty. This penalty functions like interest on the amount you should have paid throughout the year, and in 2026 it runs at approximately 8% annually on the underpaid amount. (IRS — Topic 306: Penalty for Underpayment of Estimated Tax)

Common reasons people under-withhold:

• Multiple jobs. Each employer withholds as if that were your only income. The combined effect can leave you under-withheld because of bracket stacking.
• Freelance or side income. W-2 employers withhold from wages, but no one withholds from your 1099 income automatically.
• Investment income. Dividends, capital gains, and rental income are not subject to automatic withholding.
• Got divorced. Losing the MFJ filing status and the deductions that came with it can significantly increase your tax bill.
• Claimed too many deductions on an old W-4. If you claimed more allowances than your situation supports, you may have been withholding too little for years.

The IRS Safe Harbor: When You Avoid the Penalty

You will not be charged an underpayment penalty if you meet at least one of these three safe harbor rules:

The most common safe harbor people rely on is the prior-year rule: if you know your 2025 tax bill was $8,000, you just need to withhold at least $8,000 in 2026 to avoid a penalty — even if you actually owe $10,000. You’ll still owe $2,000 at filing, but no penalty. For higher earners (AGI over $150,000), the threshold rises to 110% of the prior-year bill.

Worked Example: $70,000 Salary, Three Withholding Scenarios

Let’s work through a concrete example. Say you’re a single filer earning $70,000 per year, paid biweekly (26 paychecks). First, let’s calculate your actual 2026 federal income tax liability:

Now compare what happens under three different withholding situations:

In the over-withheld scenario, that $2,738 refund came out of your biweekly paychecks at $105 extra per check. You could have had that money in hand every two weeks. In the under-withheld scenario, the $2,202 bill exceeds the $1,000 de minimis threshold, so the IRS also charges an underpayment penalty — adding roughly $90–$140 depending on when in the year the shortfall occurred.

The IRS Tax Withholding Estimator: Your Best Tool

The IRS provides a free online tool that does the heavy lifting for you: the Tax Withholding Estimator. It asks you to enter:

• Your filing status and number of dependents
• Current pay stubs from each employer (gross income, current withholding)
• Other income sources (self-employment, investments, pensions)
• Deductions you plan to claim
• Tax credits you expect to use (Child Tax Credit, education credits, etc.)

The estimator then projects your full-year tax liability, compares it to your current year-to-date withholding trajectory, and tells you whether you’re on track, over-withholding, or under-withholding. If you need to change, it outputs the exact numbers to enter on a new W-4.

The estimator works best when you run it after receiving your first few paychecks of the year (so you have real numbers to enter) and again after any major life change. It does not save your information, so it works completely anonymously — nothing is shared with the IRS from the estimator itself.

How to Adjust Your W-4

Once you know your withholding is off, fixing it is straightforward. Here’s the process:

1. Download a blank W-4 from the IRS website or ask your HR department for one.
2. Complete Step 1 (personal information) and Step 5 (signature). For a simple single-income situation, this alone may be all you need.
3. Use Step 3 to claim dependents if you have children. Entering your Child Tax Credit amount here directly reduces withholding rather than waiting for a refund.
4. Use Step 4 for other adjustments. In 4(a) enter other taxable income not from jobs (such as freelance income). In 4(b) enter extra deductions if you itemize. In 4(c) add extra dollar-per-paycheck withholding if you want a safety buffer.
5. Multiple jobs: use the IRS estimator or the Multiple Jobs Worksheet on page 3 of the W-4. This is the most common cause of under-withholding, and the worksheet accounts for the bracket stacking effect.
6. Submit the new W-4 to your payroll department. Changes typically take effect within one or two pay periods.

You can submit a new W-4 at any time — you don’t have to wait until open enrollment or the start of a new year. The IRS recommends reviewing your withholding at least once a year, and after any major life or financial event. (IRS — Check Your Withholding)

Special Situations That Require Extra Attention

Multiple Jobs or Two-Income Households

This is the single biggest cause of under-withholding. If you work two jobs that each pay $40,000, each employer withholds as though you earn $40,000 total. But your actual taxable income is $80,000 — and some of those dollars fall in a higher bracket. The IRS Multiple Jobs Worksheet on the back of the W-4 accounts for this. You only complete it for one of your jobs (your highest-paying one).

The same issue applies to married couples where both partners work. If you each claim Standard withholding on your individual W-4s, neither account for the fact that your combined income pushes some dollars into higher brackets. Checking the “Married filing jointly” box and completing the multiple jobs section fixes this.

Self-Employment or Gig Income

Income from freelance work, consulting, or platform gigs (Uber, Etsy, Upwork) is not subject to automatic withholding. You have two options to avoid a big bill and penalty:

• Increase withholding at your day job. Use Step 4(a) on your W-4 to add your expected self-employment income. Your employer will withhold more from each paycheck to cover the additional taxes.
• Pay quarterly estimated taxes. If your side income is substantial, you can make four estimated tax payments directly to the IRS each year using IRS Direct Pay or Form 1040-ES. Due dates are typically April 15, June 15, September 15, and January 15.

Investment and Passive Income

Dividends, interest, capital gains, and rental income all add to your taxable income but are not automatically withheld on. If you have meaningful investment income, add it to your W-4 in Step 4(a) or make estimated tax payments quarterly. (IRS — Estimated Taxes)

Quick Reference: Signs Your Withholding Is Off

The Bottom Line

The goal of tax withholding is to match your prepayments as closely as possible to your actual tax liability. A small refund or a small balance due (under $1,000) is perfectly fine — that’s the target. A large refund means you let the government hold your money without paying you interest. A large balance due means you’re risking an underpayment penalty.

The fix is almost always a W-4 update, and it takes about 10 minutes using the IRS Tax Withholding Estimator to find the right numbers. Run it once a year — especially after any major life event — and you’ll avoid both the over-paid surprise and the under-paid penalty.

Sources

• IRS — Publication 505: Tax Withholding and Estimated Tax
• IRS — Tax Withholding Estimator
• IRS — Topic 306: Penalty for Underpayment of Estimated Tax
• IRS — Check Your Withholding
• IRS — About Form W-4, Employee’s Withholding Certificate
• IRS — Estimated Taxes
• IRS — Filing Season Statistics
• IRS — Direct Pay