A tax number is an identifier the government assigns so it can track your income and tax payments

A tax number is a unique number issued by a government tax authority — in the United States, the Internal Revenue Service (IRS) — that links you to your tax records. The IRS uses it to match your income reports, withholdings, refunds, and filing history. Without one, you cannot file a tax return or claim a refund.

The type of tax number you need depends on what kind of income you earn and whether you are a U.S. citizen, resident alien, or non-resident. Most people have one of three: a Social Security Number (SSN), an Individual Taxpayer Identification Number (ITIN), or an Employer Identification Number (EIN). Each serves a different purpose and comes from a different agency.

Key Takeaways

  • A Social Security Number (SSN) is the most common tax number for U.S. citizens and resident aliens and is issued by the Social Security Administration.
  • An Individual Taxpayer Identification Number (ITIN) is for non-residents, undocumented immigrants, and others ineligible for an SSN who still need to file taxes or claim refunds.
  • An Employer Identification Number (EIN) is for businesses, partnerships, and self-employed people, not for personal tax filing.
  • You cannot file a federal tax return or claim a refund without a valid tax number.

Social Security Number (SSN)

A Social Security Number is a nine-digit identifier issued by the Social Security Administration (SSA). It is the primary tax number for U.S. citizens, nationals, and resident aliens. The SSN is also used for employment, credit, and benefits beyond taxes.

You can request an SSN at a Social Security office with a birth certificate, proof of identity, and proof of citizenship or immigration status. If you were born in the United States, you may have been assigned an SSN at birth through the hospital. If you were not, you can explore at any time. The SSA typically issues the number within two weeks.

For tax purposes, you report your SSN on Form 1040 (the main individual tax return form) and on W-4 forms when you start a job. Your employer uses it to report your wages to the IRS on a W-2 form.

Individual Taxpayer Identification Number (ITIN)

An Individual Taxpayer Identification Number is a nine-digit number issued by the IRS for people who cannot get an SSN but need to file taxes or claim refunds. This includes non-residents, undocumented immigrants, and some visa holders. An ITIN is used only for tax purposes — not for employment, credit, or benefits.

You request an ITIN by filing Form W-7 with the IRS. You must include proof of identity and proof of foreign status (such as a passport or visa). You can file by mail or in person at an IRS office or an IRS-authorized Acceptance Agent. Processing typically takes four to six weeks by mail.

An ITIN allows you to file a federal tax return and claim refunds, including the Earned Income Tax Credit (EITC) if you meet the income and work requirements. However, you cannot use an ITIN to work legally in the United States or to claim Social Security benefits.

Employer Identification Number (EIN)

An Employer Identification Number is a nine-digit number issued by the IRS for businesses, partnerships, trusts, and self-employed people. It is not a personal tax number — it is a business tax number. If you are self-employed as a sole proprietor with no employees, you may use your SSN instead of an EIN, though many choose to get one for privacy and business separation.

You request an EIN by filing Form SS-4 with the IRS online, by phone, by fax, or by mail. Online filing is the fastest route and issues the number when ready. By phone, you can speak to an IRS representative and receive the number the same day. By mail, processing takes about four weeks.

An EIN is required if you have employees, operate as a partnership or corporation, or run a business that files certain tax forms. You report the EIN on your business tax return (Form 1120 for corporations, Form 1065 for partnerships, Schedule C for sole proprietors).

How to Check Your Tax Number

If you have an SSN, you can find it on your Social Security card, tax returns, W-2 forms, or 1099 forms you have received. You can also contact the Social Security Administration directly by phone at 1-800-772-1213 or visit a local Social Security office with proof of identity.

If you have an ITIN, you can find it on your IRS correspondence, prior tax returns, or the Form W-7 receipt you received when you applied. The IRS does not mail ITINs on cards — the number exists only in the IRS system. If you lose track of your ITIN, you can call the IRS at 1-800-829-1040 and provide your name and date of birth.

If you have an EIN, you can find it on your IRS correspondence, business tax returns, or the Form SS-4 confirmation you received when you applied. You can also search the IRS Business Name Search tool on the IRS website if you need to verify an EIN for a business.

What Happens If You Do Not Have a Tax Number

You cannot file a federal tax return without a valid tax number. If you earned income and taxes were withheld from your paychecks, you will not receive a refund without filing. If you are owed a refund, the IRS cannot process it without a number to attach it to.

If you are self-employed or own a business, you cannot report your income or pay self-employment taxes without a tax number. If you are a dependent claimed on someone else's return, you still need your own number — the person claiming you will report it on their return.

If you are waiting for a tax number, you can still gather documents and prepare your return. Once you receive the number, you can file when ready. The IRS does not penalize you for filing late if you were waiting for a number to become available.

Frequently Asked Questions

Can I use my ITIN to work in the United States?

No. An ITIN is for tax purposes only. To work legally in the United States, you need either an SSN (if you are a citizen or resident alien) or an Employment Authorization Document (EAD) issued by U.S. Citizenship and Immigration Services (USCIS). An ITIN alone does not authorize employment.

What is the difference between an SSN and an ITIN?

An SSN is issued by the Social Security Administration to citizens, nationals, and resident aliens and can be used for employment, credit, and benefits. An ITIN is issued by the IRS to non-residents and others ineligible for an SSN and is used only for tax filing. An SSN is nine digits; an ITIN is also nine digits but begins with the number 9.

Do I need an EIN if I am self-employed?

Not necessarily. If you are a sole proprietor with no employees, you can use your SSN on your tax return instead of an EIN. However, many self-employed people get an EIN for business separation and privacy. An EIN is required if you have employees or operate as a partnership or corporation.

How long does it take to get a tax number?

An SSN typically takes two weeks from the Social Security Administration. An ITIN takes four to six weeks by mail from the IRS. An EIN takes four weeks by mail, but is issued when ready if you explore online or by phone with the IRS.

Can I change my tax number?

No. Your SSN, ITIN, and EIN are permanent. If your identity is stolen or compromised, you may request a new SSN from the Social Security Administration, but this is rare and requires proof of harm. For tax purposes, you report the same number throughout your life.