Starting a new job in the United States means filling out at least two tax-related forms before your first paycheck, and knowing how to fill out tax forms for a new job comes down to three documents: IRS Form W-4 for federal income tax withholding, Form I-9 for employment eligibility, and, in most states, a separate state withholding form. Get them right on day one and your paychecks arrive accurate. Get them wrong and you either lose take-home pay to over-withholding or face a bill next April.
What to Gather Before Your First Day
Have these ready before you sit down with the paperwork:
- Your Social Security number, plus the numbers for any dependents you plan to claim on your W-4.
- A government-issued ID. A passport, driver’s license, or another document from the I-9 acceptable documents lists.
- Your current home address, which determines the state and local taxes that apply to your wages.
- Your filing status for the year: single, married filing jointly, married filing separately, or head of household.
- Your most recent tax return, which helps you estimate income and check whether last year’s withholding was accurate.
Missing even one item can stall onboarding or lead to data-entry errors on your earliest paychecks.
Filling Out Form W-4 Step by Step
The W-4 tells your employer how much federal income tax to withhold from each paycheck. It has five steps, and most people only need to complete Steps 1 and 5.
Step 1: Personal Information and Filing Status
Enter your legal name, address, and Social Security number, then check the box for your filing status. That status sets the standard deduction and tax bracket structure your employer’s payroll system uses. Pick the status you actually expect to use when you file. Choosing the wrong one here is one of the most common causes of over- or under-withholding.
Step 2: Multiple Jobs or a Working Spouse
Complete Step 2 if you work more than one job at a time, or if you’re married filing jointly and your spouse also works. Without it, each employer withholds as if its paycheck is your only income, and you end up under-withheld overall. The IRS Tax Withholding Estimator at apps.irs.gov walks you through the calculation and tells you what to enter. The W-4 also includes a paper worksheet, but the online tool handles complex situations better.
Step 3: Claiming Dependents
For 2026, multiply each qualifying child under age 17 by $2,200 and each other dependent by $500, then enter the total. This reduces your withholding each pay period to reflect the credits you’ll claim on your return. If your income exceeds $200,000 as a single filer or $400,000 filing jointly, the credits begin to phase out, and the W-4 instructions include an adjustment for higher earners.
Step 4: Optional Adjustments
Step 4 covers three situations the earlier steps miss. Line 4(a) is for non-job income like interest, dividends, or rental income; entering an amount here tells payroll to withhold extra so you don’t owe a lump sum in April. Line 4(b) reduces withholding if you plan to itemize deductions rather than take the standard deduction. Line 4(c) is a straight “withhold this much extra per paycheck” field, useful if you’ve been burned by a tax bill and want a cushion.
Step 5: Signature
Sign and date the form. The signature certifies under penalty of perjury that everything on the W-4 is accurate. Submitting a W-4 with false information to reduce your withholding carries a $500 civil penalty per occurrence, separate from any taxes and interest you’d owe.
If You Skip the W-4
Federal rules require your employer to withhold as if you’re a single filer with no adjustments on Steps 2 through 4. That usually means heavier withholding than you need. You’ll get the excess back as a refund when you file, but you lose months of take-home pay in the meantime.
Claiming Exemption from Withholding
You can claim complete exemption from federal income tax withholding only if you owed zero federal income tax last year and expect to owe zero this year. On the 2026 W-4, check the exemption box, complete Steps 1(a), 1(b), and 5, and skip the rest. The exemption expires each year, so file a new W-4 by February 16 of the following year or your employer reverts to default withholding.
Completing Form I-9 and Bringing the Right Documents
Form I-9 proves you’re legally authorized to work in the United States, and it has hard deadlines.
Section 1: Your Attestation
You complete Section 1 no later than your first day of work, meaning the day you actually start performing duties for pay. You can fill it out earlier, after accepting the job offer, but never before. Section 1 asks for your name, address, date of birth, and an attestation of your citizenship or immigration status.
Section 2: Documents Your Employer Reviews
Your employer must examine your original documents and complete Section 2 within three business days of your start date. Acceptable documents fall into three lists:
- List A documents prove both identity and work authorization in a single item, such as a U.S. passport or permanent resident card.
- List B documents prove identity only, such as a state driver’s license or government-issued ID card.
- List C documents prove work authorization only, such as a Social Security card or birth certificate.
You present either one document from List A, or one from List B paired with one from List C. Expired documents don’t count. Your employer cannot tell you which specific documents to present or reject a valid document because they’d prefer a different one. If you can’t produce acceptable documents within the three-day window, your employment can be delayed or rescinded.
State and Local Withholding Forms
Nine states impose no state income tax at all. If you work in one of them, you can skip this. Everyone else likely needs at least one additional withholding form for the state where they work.
Some states accept the federal W-4 and calculate state withholding from your federal elections. Others require their own form with state-specific fields. Your employer’s payroll department should hand you the correct form during onboarding. Ask directly if you’re unsure, because failing to submit a state form triggers maximum withholding the same way skipping the federal W-4 does.
Living in One State and Working in Another
If you commute across state lines, you may owe income tax to both states unless they have a reciprocity agreement. Where reciprocity exists, you pay income tax only to your home state and file a withholding exemption form with the work state so its taxes aren’t deducted. Without reciprocity, you’ll file returns in both states and claim a credit in your home state for taxes paid to the work state. Ask payroll which forms to complete for your situation. Getting this wrong means either double-withholding all year or a surprise bill at tax time.
FICA on Your Pay Stub
The W-4 controls federal income tax withholding, not FICA. Social Security and Medicare come out of every paycheck automatically, and there’s no form to adjust them.
For 2026, Social Security tax is 6.2% on wages up to $184,500. Once your year-to-date earnings pass that ceiling, the Social Security deduction stops for the rest of the year. Medicare tax is 1.45% with no cap. If your wages exceed $200,000 in a calendar year, your employer withholds an additional 0.9% Medicare tax on everything above that threshold.
Combined, the standard employee share of FICA is 7.65% of gross pay. Your employer pays an equal 7.65%, which doesn’t appear on your pay stub. On your first check, the FICA lines should show exactly 6.2% and 1.45% of your gross wages.
Updating Your W-4 After Life Changes
Your W-4 isn’t a set-it-and-forget-it document. The IRS flags these events as triggers to file a new one:
- Marriage or divorce, which changes your filing status, tax brackets, and standard deduction.
- Birth or adoption of a child, which adds to your Step 3 credits.
- Buying a home, since mortgage interest may make itemizing worthwhile and affect Step 4(b).
- Starting or losing a second job, which changes the Step 2 calculation.
- Significant changes in non-wage income, like new investment, rental, or retirement distributions that affect Step 4(a).
After marriage, the IRS advises submitting a new W-4 within 10 days. Even without a strict deadline, checking your withholding after any major change prevents the slow accumulation of errors that becomes a four-figure surprise in April. The IRS Tax Withholding Estimator takes about 15 minutes and tells you exactly what to adjust.
Checking Your First Paycheck
Most employers accept forms through a secure digital payroll portal, though some still use paper through HR. The I-9 has the tightest deadline: Section 1 by your first day, Section 2 within three business days after. Submit your W-4 and any state form before your first payroll run so default withholding doesn’t kick in.
When your first pay stub arrives, verify three things: that federal withholding matches your W-4 elections, that FICA shows 6.2% for Social Security and 1.45% for Medicare, and that state tax matches what you expected. A data-entry error caught on the first check is a minor fix. The same error left alone for six months follows you into tax season. If something looks off, bring it to payroll with your copies of the submitted forms so you can pinpoint where the numbers diverge.