W-4

The IRS form employees complete to tell their employer how much federal income tax to withhold from each paycheck.

A W-4 (Employee's Withholding Certificate) is the IRS form that tells your employer how much federal income tax to withhold from your paycheck. When you start a new job, your employer is required to have you complete a W-4 before your first paycheck. The information you provide — filing status, number of dependents, additional income sources, and any extra withholding requested — determines how much federal tax is taken out each pay period. If you do not submit a W-4, employers are required to withhold at the highest single rate with no adjustments.

The W-4 was redesigned in 2020 to align more closely with how federal taxes are actually calculated. The new form replaced allowances with a more direct approach: you report expected additional income (from a second job or investments), expected deductions beyond the standard deduction, and the number of qualifying dependents. This more closely matches your actual expected tax liability and reduces the likelihood of a large refund or an unexpected tax bill — both of which indicate inaccurate withholding.

Your W-4 is not filed with the IRS — it stays with your employer. However, the IRS can require your employer to submit it if the IRS suspects underreporting. You can update your W-4 at any time during the year, and it is good practice to review it after major life events: marriage, divorce, birth of a child, significant income changes, or taking on a second job. The IRS Tax Withholding Estimator tool is a reliable way to check whether your current withholding is accurate before reviewing your W-4.

Many employees misunderstand the W-4 as a document that determines whether they get a refund. The W-4 only controls withholding — the amount pre-paid toward your tax liability each paycheck. Whether you get a refund or owe taxes at filing depends on your total tax liability versus total taxes withheld across the year. A large refund is not free money — it is an interest-free loan you made to the government. Adjusting your W-4 to withhold more accurately is financially better than deliberately over-withholding and waiting for an April refund.

When to Update Your W-4

  • Starting a new job — complete and submit a W-4 before your first paycheck.
  • Getting married or divorced — your filing status and combined household income affect your marginal rate significantly.
  • Having a child or gaining a dependent — the child tax credit and dependent credits reduce your liability and should be reflected in withholding.
  • Taking a second job or significant side income — additional income can push you into a higher bracket; under-withholding on one income source leads to a tax bill.
  • Major income changes — a large raise, a stock sale, or a significant bonus can increase your liability beyond what your existing W-4 accounts for.
  • Significant itemized deductions — if you expect to itemize (large mortgage interest, charitable contributions), you can claim those deductions on the W-4 to reduce withholding.

Common W-4 Mistakes

  • Never updating it after starting: using the same W-4 for years despite major life changes leads to inaccurate withholding in either direction.
  • Claiming exempt when you are not: claiming exempt means zero withholding — only valid if you had no tax liability last year and expect none this year.
  • Ignoring the multiple jobs worksheet: households with two earners often underwithold on each job individually because each job withholds based on a single-income assumption.
  • Confusing withholding with tax liability: a W-4 change does not change how much tax you owe — it only changes when you pay it (per paycheck vs. at filing).
  • Failing to account for investment or self-employment income: wages-only withholding does not cover capital gains, dividends, or freelance income — estimated quarterly taxes may be needed.
  • Over-withholding intentionally for a 'forced savings' refund: this is an interest-free loan to the government; redirecting that money to a high-yield account is financially more effective.

Example

A single earner starts a new job and completes a W-4 marking single filing status with no adjustments. Midyear, she gets married and her spouse also earns income. She updates her W-4 using the IRS Withholding Estimator, which recommends additional withholding to prevent an underpayment penalty given their combined income bracket.