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

When you start a new job in the United States, two federal forms are mandatory before your first paycheck: IRS Form W-4, which sets your federal income tax withholding, and USCIS Form I-9, which verifies you’re legally authorized to work. Most people also complete a state withholding form, a direct deposit authorization, and benefits enrollment paperwork during onboarding. The full list of tax forms to fill out when starting a new job depends on where you live, what your employer offers, and whether you’re being hired as an employee or an independent contractor.

Form W-4: Federal Income Tax 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 doesn’t use allowances. You work through numbered steps that account for filing status, dependents, other income, and deductions, skipping any step that doesn’t apply.

Step 1: Personal Information and Filing Status

You provide your name, address, and Social Security number, then choose the filing status you’ll use on your tax return: Single or Married Filing Separately, Married Filing Jointly (or Qualifying Surviving Spouse), or Head of Household.¹ This choice sets the baseline for every other calculation, so it should match what you actually plan to file. Head of Household applies only if you’re unmarried and pay more than half the cost of keeping a home for a qualifying dependent.

Step 2: Multiple Jobs or a Working Spouse

Complete this step if you hold more than one job at the same time, or if you’re married filing jointly and your spouse also works.¹ Without it, each employer withholds as if its paycheck were your only income, which almost guarantees a balance due in April. The IRS Tax Withholding Estimator at irs.gov produces the most accurate result.

For two jobs with roughly similar pay, checking the box in Step 2(c) on both W-4s is a simpler shortcut. It tells both payroll systems to withhold at a higher rate. This tends to over-withhold, which produces a refund rather than a bill. When pay levels differ significantly, use the estimator or the Multiple Jobs Worksheet on page 3 of the form.

Step 3: Credits for Dependents

Step 3 lowers 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 if filing jointly), multiply the number of qualifying children by $2,200 and enter the result on line 3(a).¹ Up to $1,700 per child can come back to you as a refundable credit even if you owe no tax.

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

Step 4: Other Income, Deductions, and Extra Withholding

Step 4 has three optional lines for fine-tuning:

Line 4(a) is for other income that isn’t from a job, such as interest, dividends, or retirement distributions. Enter the estimated annual total, and your employer spreads the additional withholding across your paychecks. This usually removes the need for quarterly estimated payments on that income.¹
Line 4(b) is for deductions above the standard deduction. For 2026, the standard deduction is $16,100 for Single filers, $24,150 for Head of Household, and $32,200 for Married Filing Jointly. Leave this blank unless you’re confident you’ll itemize; the standard deduction is already built into the withholding tables.³
Line 4(c) is for a flat dollar amount of extra withholding per paycheck. Use it to cover situations the earlier steps miss, or if you simply want a cushion against owing in April.

Form I-9: Employment Eligibility Verification

The I-9 is not a tax form. It verifies your identity and legal authorization to work, and every employer must complete one for every new hire.⁴ Unlike most onboarding paperwork, it involves physical document inspection rather than data entry alone.

What You Complete

You fill out Section 1 no later than your first day of work, though you can complete it any time after accepting the offer.⁵ You provide your legal name, date of birth, and address, and attest to your citizenship or immigration status. Your employer cannot fill this section out for you.

What Your Employer Completes

Within three business days of your start date, your employer must physically examine original, unexpired documents that establish your identity and work authorization.⁵ For jobs lasting less than three business days, this must happen by your first day.

Which Documents to Bring

You choose which documents to present from three lists published by USCIS:⁶

A single List A document proves both identity and work authorization. Examples include a U.S. passport, a Permanent Resident Card, or an Employment Authorization Document with a photo.
If you don’t have a List A document, you present one from List B (identity) plus one from List C (work authorization). A common pairing is a state driver’s license with a Social Security card or birth certificate.

Your employer cannot tell you which documents to present or reject valid documents in favor of others. Doing so is discrimination under federal law.

Remote Verification

Employers enrolled in E-Verify can use an alternative procedure for remote employees. The employer reviews copies of your documents and then holds a live video call where you display the originals on camera.⁷ The employer retains clear copies and notes on the I-9 that the alternative procedure was used. Employers not enrolled in E-Verify must still examine documents in person, even for remote workers.

State and Local Withholding Forms

If you work in a state with an income tax, you’ll almost always complete a separate state withholding form alongside your W-4. These forms collect similar information (filing status, dependents, exemptions) but apply state-specific rates and brackets. Roughly 40 states plus the District of Columbia have a broad individual income tax. A few states use the federal W-4 for state purposes; nine have no individual income tax and require no state withholding form.

Some cities and counties impose local income taxes as well, which means an additional withholding form. Your employer should identify what applies based on where you live and where you physically work.

Living in One State and Working in Another

Cross-border commuters could theoretically owe income tax in both states. Many neighboring states have reciprocity agreements that limit tax to your home state, and your employer withholds accordingly. You’ll usually need to file an exemption form with your employer to activate it; otherwise the employer may default to withholding for the work state. Ask HR whether a reciprocity agreement covers your situation before your first paycheck.

Benefits Enrollment and Retirement Contributions

These aren’t tax forms in the strict sense, but the elections you make during onboarding change your paycheck and your tax bill. Most employers give new hires a window, often 30 days, to enroll.

Traditional 401(k) contributions come out before federal income tax is calculated, reducing your taxable income for the year. The 2026 employee contribution limit is $24,500. A Roth 401(k), if offered, uses after-tax dollars, with qualified retirement withdrawals coming out tax-free.⁸
A Health Savings Account is available if you enroll in a high-deductible health plan. The 2026 contribution 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.⁹
Employer-sponsored health insurance premiums are typically deducted pre-tax under a Section 125 cafeteria plan, reducing both income tax and FICA withholding.

You can adjust these later, but setting them at hire captures the full year of tax benefits. Waiting three months to start 401(k) contributions forces larger per-paycheck deferrals to hit the same annual total.

Direct Deposit Authorization

Nearly every employer collects a direct deposit form during onboarding. It asks for your bank’s routing number, your account number, and the account type. Some employers let you split each paycheck across multiple accounts, which is useful for automatic savings. Skipping this may leave you receiving paper checks, which can delay when your pay actually clears.

If You’re an Independent Contractor Instead

Everything above applies to employees. Contractors fill out different paperwork. Instead of a W-4, you complete Form W-9, which supplies your taxpayer identification number to the company paying you.¹⁰ No taxes are withheld. You pay your own income tax and self-employment tax through quarterly estimated payments.

What Happens 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, which is the most aggressive default.¹¹ Take-home pay will be lower than a properly completed form would produce. Submitting the W-4 fixes it, though the first paycheck or two may still reflect the default rate before the correction takes effect.

Updating Your Forms After Onboarding

You can submit a new W-4 to your employer at any time during the year.¹ Common triggers include 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. Reviewing your W-4 once a year is worthwhile. A form filled out on day one and never touched again is the most common reason people are surprised by what they owe in April.

1
IRS. Form W-4 2026 Employee’s Withholding Certificate
2
Internal Revenue Service. Child Tax Credit
3
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill
4
U.S. Citizenship and Immigration Services. I-9, Employment Eligibility Verification
5
U.S. Citizenship and Immigration Services. 2.0 Who Must Complete Form I-9
6
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)
8
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
9
Internal Revenue Service. Expanded Availability of Health Savings Accounts – Notice 26-05
10
Internal Revenue Service. Forms and Associated Taxes for Independent Contractors
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Office of the Law Revision Counsel. 26 U.S. Code 3402 – Income Tax Collected at Source