What Tax Form Do You Fill Out When You Start a Job?

When you start a new job in the United States, the two tax forms you fill out are IRS Form W-4, which sets your federal income tax withholding, and USCIS Form I-9, which proves you’re legally allowed to work. Most people also complete a state withholding form, a direct deposit authorization, and a benefits enrollment packet during the same onboarding session. Getting the W-4 right is the one that most affects your paycheck and your April tax bill.

Form W-4: Your Federal Withholding

Form W-4, the Employee’s Withholding Certificate, tells your employer how much federal income tax to pull from each paycheck.¹ The current version no longer uses allowances. You work through a short series of steps, and you can skip the ones that don’t apply.

Step 1: Who You Are and How You File

You give your name, address, and Social Security number, then choose a filing status: Single or Married Filing Separately, Married Filing Jointly or Qualifying Surviving Spouse, or Head of Household.¹ Pick the status you actually plan to file under. Head of Household applies only if you’re unmarried and pay more than half the cost of keeping up a home for a qualifying dependent.

Step 2: Multiple Jobs or a Working Spouse

This step matters if you hold more than one job at the same time, or you’re married filing jointly and your spouse works too.¹ Without it, each employer withholds as if its paycheck is your only income, and you’ll almost certainly owe in April. The IRS Tax Withholding Estimator at irs.gov is the most accurate way to handle it.

If you have exactly two jobs with roughly similar pay, the simpler option is checking the box in Step 2(c) on both W-4s. Both payrolls then withhold at a higher rate. This tends to over-withhold, so you’ll see a bigger refund and smaller paychecks all year. When one job pays significantly more than the other, use the estimator or the Multiple Jobs Worksheet on page 3 of the form.

Step 3: Credits for Dependents

Step 3 reduces your withholding to reflect the Child Tax Credit and the Credit for Other Dependents. For 2026, the Child Tax Credit is worth up to $2,200 per qualifying child under age 17.² If your total income will be $200,000 or less ($400,000 or less filing jointly), multiply each qualifying child by $2,200 and enter the result on line 3(a).¹ Up to $1,700 per child can come back as a refundable credit even if you owe no federal income tax.

The Credit for Other Dependents covers dependents who don’t qualify for the Child Tax Credit, typically children 17 and up or qualifying relatives. It’s worth $500 per dependent and goes on line 3(b).² Add 3(a) and 3(b) together for your line 3 total.

Step 4: Fine-Tuning

Step 4 has three optional lines:

Line 4(a), Other income. If you earn money outside of a job, such as interest, dividends, or retirement distributions, enter the estimated annual total. Your employer spreads the extra withholding across your paychecks, which usually removes the need for quarterly estimated payments on that income.¹
Line 4(b), Deductions. Use this only if you plan to itemize and your deductions will exceed the standard deduction for your filing status. For 2026, the standard deduction is $16,100 for Single filers, $24,150 for Head of Household, and $32,200 for Married Filing Jointly. If you’re not sure, leave it blank. The standard deduction is already built into the withholding tables.³
Line 4(c), Extra withholding. A flat dollar amount pulled from every paycheck on top of the calculated withholding. Useful if you want a buffer against owing anything in April.

What Happens If You Get It Wrong

Under-withholding means you’ll owe when you file, and a large shortfall adds an underpayment penalty on top.⁴ Over-withholding produces a refund, which just means you lent the government money interest-free all year. Honest mistakes aren’t a legal problem, but willfully putting false information on a W-4 to reduce withholding can carry a fine of up to $1,000, up to a year in prison, or both.⁵

Form I-9: Proving You Can Work

The I-9 has nothing to do with taxes. It verifies your identity and your legal right to work in the country, and every employer must complete one for every new hire.⁶ It involves physical document inspection, so you can’t just key numbers into a portal.

Section 1 Is Yours

You fill out Section 1 by your first day of work, though you can complete it anytime after accepting the offer.⁷ You provide your legal name, date of birth, and address, then attest to your citizenship or immigration status. Your employer can’t fill it out for you.

Section 2 Is Your Employer’s, Within Three Days

Within three business days of your start date, your employer must physically examine original, unexpired documents that prove your identity and work authorization.⁷ For a job lasting less than three business days, everything must be done by your first day.

Which Documents to Bring

You choose which documents to present from three lists published by USCIS:⁸

List A, one document that proves both identity and work authorization. A U.S. passport, Permanent Resident Card, or Employment Authorization Document with photo all qualify on their own.
List B plus List C, one from each. A common pairing is a state driver’s license (List B) plus a Social Security card or birth certificate (List C).

Your employer cannot tell you which documents to present or reject valid ones because they’d prefer to see something else. That’s considered discrimination under federal law.

If You Work Remotely

Employers enrolled in E-Verify can use an alternative procedure for remote employees. The employer reviews copies of your documents and then conducts a live video call where you hold up the originals on camera.⁹ If your employer doesn’t participate in E-Verify, the traditional in-person examination still applies even if you work from home.

State (and Sometimes Local) Withholding Forms

If you work in a state with an income tax, you’ll almost certainly fill out a separate state withholding form alongside your W-4. These forms ask for similar information using state-specific rates and brackets. About 40 states and the District of Columbia collect a broad individual income tax. A handful simply use a second copy of the federal W-4 for state purposes. Nine states have no individual income tax, so there’s no state form at all.

Some cities and counties also impose a local income tax, which can mean yet another form. Your employer should tell you which ones apply based on where you live and where you physically work.

Living in One State, Working in Another

Commuters can theoretically owe tax in both states. Many neighboring states have reciprocity agreements that prevent that result, so you only owe income tax to your home state and your employer withholds accordingly. You usually need to file an exemption form with your employer to activate the agreement. Without it, the employer may default to withholding for the work state and leave you to sort it out at tax time. Ask HR before your first paycheck.

Social Security and Medicare: Automatic, No Form

No form you fill out controls these. Social Security and Medicare taxes, collectively FICA, come out of every paycheck at fixed federal rates. Social Security is 6.2% on earnings up to $184,500 in 2026, and Medicare is 1.45% on all earnings with no cap.¹⁰ Your employer matches both. If you earn above $200,000 ($250,000 married filing jointly), an additional 0.9% Medicare surtax applies to wages above those thresholds, and the employer does not match that extra portion. You don’t fill anything out for any of it.

Benefits Enrollment Affects Your Paycheck Too

Benefits elections aren’t tax forms, but the choices you make reshape your taxable income. Most employers give new hires about 30 days to enroll.

401(k) or similar retirement plan. Traditional 401(k) contributions come out before federal income tax is calculated, lowering your taxable income. The maximum employee contribution for 2026 is $24,500. A Roth 401(k), if offered, uses after-tax dollars but produces tax-free qualified withdrawals in retirement.¹¹
Health Savings Account. If you enroll in a high-deductible health plan, you may be eligible to contribute to an HSA. The 2026 limit is $4,400 for self-only coverage and $8,750 for family coverage, contributions are pre-tax, and withdrawals for qualified medical expenses are tax-free.¹²
Health insurance premiums. Most employer-sponsored premiums are deducted pre-tax under a Section 125 cafeteria plan, which reduces both your income tax and FICA withholding.

You can usually change contribution levels later, but starting right means you capture the full annual tax benefit. Delaying 401(k) enrollment by three months forces larger per-paycheck contributions the rest of the year to hit the same total.

Direct Deposit

Nearly every employer asks you to set up direct deposit during onboarding. The form needs your bank’s routing number, your account number, and the account type. Some employers let you split deposits across multiple accounts, which is useful for routing part of each paycheck into savings automatically. Without it, you may get paper checks, which can delay when the money actually arrives.

If You’re a Contractor, Not an Employee

Everything above applies to employees. If a company hires you as an independent contractor, you fill out Form W-9 instead of a W-4, no taxes are withheld, and you pay your own income tax and self-employment tax through quarterly estimated payments.¹³ No I-9 either. If a company is calling you a contractor but directing your daily work, setting your hours, and providing your equipment, you may actually be a misclassified employee entitled to withholding and employer FICA contributions.¹⁴

If You Don’t Submit a W-4

Your employer won’t guess. Federal law requires them to withhold as if you’re a single filer with no other adjustments, the most aggressive default.¹⁵ That means noticeably smaller take-home pay. The fix is just submitting the form, but your first paycheck or two may already reflect the higher rate before the correction catches up.

Updating the W-4 Later

You can submit a new W-4 to your employer at any time during the year.¹ Common triggers are marriage, divorce, a new child, a second job, or a significant change in non-wage income. Your employer adjusts withholding starting with the next applicable payroll cycle. Revisit it at least once a year. Many people fill one out on their first day, never touch it again, and are surprised by a $2,000 bill in April.

1
IRS. Form W-4 2026 Employee’s Withholding Certificate
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Internal Revenue Service. Child Tax Credit
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Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill
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Internal Revenue Service. Interest Rates Remain the Same for the First Quarter of 2026
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Office of the Law Revision Counsel. 26 U.S. Code 7205 – Fraudulent Withholding Exemption Certificate or Failure to Supply Information
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U.S. Citizenship and Immigration Services. I-9, Employment Eligibility Verification
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U.S. Citizenship and Immigration Services. 2.0 Who Must Complete Form I-9
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U.S. Citizenship and Immigration Services. Form I-9 Acceptable Documents
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U.S. Citizenship and Immigration Services. Remote Examination of Documents (Optional Alternative Procedure to Physical Document Examination)
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Internal Revenue Service. Social Security and Medicare Withholding Rates
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Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
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Internal Revenue Service. Expanded Availability of Health Savings Accounts – Notice 26-05
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Internal Revenue Service. Forms and Associated Taxes for Independent Contractors
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Internal Revenue Service. Independent Contractor (Self-Employed) or Employee?
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Office of the Law Revision Counsel. 26 U.S. Code 3402 – Income Tax Collected at Source