A tax number is an identifier the government assigns to you or your business so they can track income, taxes paid, and tax filings

The term "tax number" covers several different identifiers depending on who you are and what you do. If you work as an employee, your tax number is your Social Security Number (SSN). If you're self-employed or run a business, you may have an Employer Identification Number (EIN), also called a Federal Tax ID. If you're a sole proprietor without employees, you can use your SSN instead. Nonprofits, trusts, and certain other entities get their own EINs. The IRS uses these numbers to match your income reports to your tax returns and to enforce tax law.

You don't apply for a tax number in the way you might apply for a loan or a permit. Your SSN is issued by Social Security when you're born or when you first enter the country legally. An EIN is issued by the IRS when you register your business, usually through Form SS-4. Both are free and permanent — you keep the same number for life unless you're a victim of identity theft and the IRS issues you a new one.

Key Takeaways

  • Your Social Security Number is your tax number if you work as an employee; self-employed people and business owners typically need an Employer Identification Number instead.
  • The IRS uses your tax number to track income reported by employers or clients and to match it against the tax return you file.
  • You receive your Social Security Number automatically; you request an EIN by filing Form SS-4 with the IRS, either online or by mail.
  • Banks, employers, and clients will ask for your tax number before they can pay you or report your income to the government.

Social Security Number versus Employer Identification Number

A Social Security Number is a nine-digit identifier issued by the Social Security Administration. It's tied to your name and date of birth. If you work as an employee — meaning someone else withholds taxes from your paycheck — your SSN is your tax number. Your employer reports your wages to the IRS using your SSN, and you use it when you file your individual tax return.

An Employer Identification Number is a nine-digit number issued by the IRS. It's tied to a business entity, not to you personally. You need an EIN if you're self-employed and have a business name separate from your legal name, if you have employees, if you operate as a partnership or corporation, or if you run a nonprofit. Some self-employed people use their SSN instead of an EIN, but many choose to get an EIN to keep business and personal finances separate on tax records.

The key difference: your SSN follows you as a person; an EIN follows a business. You can have one SSN but multiple EINs if you own multiple businesses.

When you need to provide your tax number

Your employer will ask for your SSN before your first paycheck. They use it to report your wages on a W-2 form at the end of the year. If you're self-employed, anyone who pays you more than $600 in a year is required to report that payment to the IRS using your tax number — either your SSN or your EIN — on a Form 1099-NEC or 1099-MISC.

Banks ask for your tax number when you open a business account or a savings account that earns interest. Landlords sometimes ask for it when you sign a lease, though they're not required to have it. If you're applying for a loan, a mortgage, or a credit card, the lender will ask for your SSN so they can check your credit history and report the account to credit bureaus.

Clients or customers who pay you for services — freelance work, consulting, contracting — will ask for your tax number so they can report the payment correctly. If you refuse to provide it, they may not be able to pay you, or they may report the payment without it, which can create problems when you file your taxes.

How to get an Employer Identification Number

You request an EIN by filing Form SS-4 with the IRS. You can do this online at irs.gov, by phone, by fax, or by mail. The online method is fastest — you fill out the form and receive your EIN immediately. By phone, you speak to an IRS representative and get your number the same day. By fax or mail, it takes one to two weeks.

You'll need to provide your legal name, the business name (if different), the business address, the type of business structure (sole proprietor, partnership, corporation, nonprofit, etc.), and the reason you're requesting an EIN. You do not need to have already filed any business paperwork or registered with your state — you can get an EIN before you officially start operating.

Once you have an EIN, write it down and keep it in a safe place. You'll use it on tax forms, business licenses, bank accounts, and loan applications. The IRS will not mail you a physical card; the number itself is your proof.

What happens if you don't have a tax number

If you're an employee and don't have an SSN, your employer cannot legally pay you or report your wages. You must have one before you can start work. If you're in the country on a visa that allows work, you can apply for an SSN through Social Security once your employer has offered you a job.

If you're self-employed and don't have an EIN, you can still use your SSN for tax purposes — many sole proprietors do. However, anyone paying you will report the payment using your SSN, which means your business income appears on your personal tax return. This is legal and common, but it doesn't separate your business finances from your personal ones on government records.

If you don't provide a tax number when someone is required to report a payment to you, they may report it as "income to unknown taxpayer" or refuse to pay you at all. This creates a mismatch between what the IRS thinks you earned and what you report on your tax return, which can trigger an audit or a notice.

Tax numbers and identity theft

Your tax number is sensitive information. Thieves can use your SSN to file a false tax return in your name and claim a refund, or to open accounts or take out loans. If you suspect your SSN has been stolen, contact the IRS immediately and file a report with the Federal Trade Commission at identitytheft.gov.

The IRS can issue you a new SSN if you're a victim of identity theft, though this is rare and requires documentation. A new number takes time to process and can create confusion with your existing tax records, so prevention — not sharing your SSN unnecessarily, monitoring your credit, and checking your tax transcript annually — is the better approach.

Frequently Asked Questions

Can I use my Social Security Number as my business tax number?

Yes. If you're self-employed and operate as a sole proprietor without employees, you can use your SSN instead of getting an EIN. Anyone paying you will report the income using your SSN, and you'll report it on your personal tax return. Many small businesses do this. Getting an EIN is optional but recommended if you want to keep business and personal finances separate on tax records.

How long does it take to get an EIN?

If you apply online at irs.gov, you receive your EIN immediately. By phone, you get it the same day. By fax or mail, it takes one to two weeks. You do not need to wait for an EIN to start your business, but you'll need one before you can open a business bank account or hire employees.

What if I lose my tax number?

You don't lose your SSN or EIN — they're permanent. If you forget your number, you can find your SSN on past tax returns, W-2 forms, or bank statements. For an EIN, check any business licenses, bank account paperwork, or previous tax filings. If you can't locate it, you can contact the IRS directly or request a new one, though this is uncommon.

Do I need a tax number to file taxes?

Yes. You must have an SSN or an Individual Taxpayer Identification Number (ITIN) to file a federal tax return. If you don't have an SSN and are not a U.S. citizen, you can apply for an ITIN through the IRS using Form W-7.