What a Tax Number Is and Why You Need One

A tax number is an identification code the government uses to track your income and tax payments

A tax number is a unique number assigned to you by the Internal Revenue Service (IRS) or your state tax authority. It connects your name to your income records, tax returns, and payments. The most common tax number is your Social Security Number (SSN), which the IRS uses to file federal taxes. Some people and businesses use other tax numbers depending on their situation — for example, a business might use an Employer Identification Number (EIN) instead of or in addition to an SSN.

You need a tax number to file a tax return, report income to your employer, open a bank account, or apply for certain government benefits. Without one, you cannot legally work in the United States or file taxes. The number stays with you for life and does not change.

Key Takeaways

Your Social Security Number is your primary tax number for federal income tax purposes.
Businesses and self-employed people may need an Employer Identification Number (EIN) in addition to or instead of an SSN.
You must have a tax number to work legally, file taxes, or open a bank account.
The IRS uses your tax number to match your income reports, W-2 forms, and 1099 forms to your tax return.
If you do not have a tax number, you can request one from the Social Security Administration or the IRS depending on your situation.

Social Security Number as your main tax identifier

Your Social Security Number (SSN) is the tax number most people use. It is a nine-digit number issued by the Social Security Administration. When you work, your employer reports your wages to the IRS using your SSN. When you file a tax return, you put your SSN on it so the IRS knows which return belongs to you.

The IRS matches your SSN to income reports from your employer (W-2 forms), banks (1099 forms for interest), and other sources. If the income reported to the IRS does not match what you reported on your tax return, the IRS will contact you. You receive an SSN when you are born or when you first move to the United States legally.

Employer Identification Number for businesses and self-employed people

An Employer Identification Number (EIN) is a tax number for businesses, partnerships, and self-employed people. It is also called a Federal Employer Identification Number (FEIN). An EIN is a nine-digit number issued by the IRS and looks similar to an SSN but serves a different purpose.

If you are self-employed and earn income from your own business, you may need an EIN. If you hire employees, you must have an EIN. Sole proprietors (people who run a business alone) can use their SSN instead of an EIN, but many choose to get an EIN to keep their personal and business finances separate. Partnerships, corporations, and nonprofits must have an EIN.

Individual Taxpayer Identification Number for people without an SSN

An Individual Taxpayer Identification Number (ITIN) is a tax number for people who do not have a Social Security Number but need to file taxes or report income in the United States. An ITIN is a nine-digit number issued by the IRS. It looks like an SSN but starts with the number 9.

You may need an ITIN if you are not a U.S. citizen or permanent resident but have income in the United States, or if you are a dependent or spouse of a U.S. citizen or resident alien. You can use an ITIN to file a tax return, open a bank account, and report income to employers. An ITIN does not give you work permission or change your immigration status — it is only for tax purposes.

How the IRS uses your tax number

The IRS uses your tax number to create a file with your name, address, and income history. Every time you file a tax return, the IRS adds it to your file. Every time your employer, bank, or client reports income in your name, that report goes into your file under your tax number.

When you file a tax return, the IRS computer system checks whether the income you reported matches the income reports already in your file. If you reported $40,000 in income but your employer reported $50,000, the IRS will send you a notice asking for an explanation. Your tax number is also used to track whether you have paid taxes in past years and whether you owe money to the IRS.

Getting a tax number if you do not have one

If you were born in the United States, you should have received an SSN as a child. If you did not, you can request one from the Social Security Administration. You will need to provide a birth certificate, proof of identity, and proof of citizenship or legal residency.

If you are not a U.S. citizen but need a tax number, you can request an ITIN from the IRS. You will need to file Form W-7 with the IRS and provide documents proving your identity and that you have a valid reason to file taxes in the United States. If you are self-employed or own a business, you can request an EIN from the IRS online, by phone, or by mail — you do not need to wait or provide as much documentation as you do for an SSN or ITIN.

Protecting your tax number

Your tax number is sensitive information. Anyone who has your tax number can file a false tax return in your name, open accounts, or commit identity theft. You should not share your tax number with anyone except your employer, your bank, your accountant, or government agencies that ask for it.

If you think someone has stolen your tax number or filed a false tax return using your name, contact the IRS immediately. You can call the IRS Identity Theft Hotline or file a report on the IRS website. The IRS can freeze your account and investigate whether a false return was filed.

Frequently Asked Questions

Is my Social Security Number the same as my tax number?

For most people, yes. Your Social Security Number is your tax number for federal income tax purposes. The IRS uses it to identify you and track your income and tax payments. However, if you own a business, you may also have an Employer Identification Number.

Do I need both an SSN and an EIN?

Not necessarily. If you are self-employed and do not hire employees, you can use your SSN on your tax return. Many self-employed people get an EIN anyway to keep their personal and business finances separate. If you hire employees or form a business entity like a corporation or partnership, you must have an EIN.

Can I change my tax number?

No. Your Social Security Number and ITIN do not change. If you get an EIN for a business, that number stays with that business. If you start a new business, you get a new EIN. You cannot request a new SSN or ITIN just because you want a different number.

What happens if I file taxes without a tax number?

The IRS will reject your return. You must have a valid tax number to file a federal income tax return. If you do not have an SSN, you must get an ITIN first. If you try to file without one, your return will not be processed and you may face penalties.

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

An ITIN is only for tax purposes. It does not give you permission to work in the United States. To work legally, you need to be a U.S. citizen, permanent resident, or have a valid work visa. Your employer will ask for your SSN or ITIN to report your wages, but that is separate from whether you are legally allowed to work.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.