What Your Tax Number Is and Why You Need It

A tax number is an identification code the government assigns to you or your business for tax purposes

The term "tax number" usually refers to one of several identification numbers the Internal Revenue Service (IRS) or your state tax authority uses to track your income and tax filings. The most common one for individuals is your Social Security Number (SSN). If you're self-employed or own a business, you may have an Employer Identification Number (EIN) instead. Some people and businesses have both. The number you use depends on how you earn income and what type of entity you operate.

You need a tax number to file income tax returns, report wages to employers, open business bank accounts, and receive certain government benefits. Without one, you cannot legally work in most jobs or file taxes. The IRS uses your tax number to match income reports from employers and financial institutions to your tax return, so they can verify you reported all your income.

Key Takeaways

Your Social Security Number is your tax number if you are an individual employee; your Employer Identification Number is your tax number if you own a business or are self-employed.
You need a tax number to work legally, file income taxes, open a business bank account, and receive benefits like Social Security or unemployment insurance.
The IRS matches your tax number to income reports from your employer and banks to verify your tax return is complete and accurate.
If you do not have a Social Security Number, you may be able to get an Individual Taxpayer Identification Number (ITIN) to file taxes and work.

Social Security Number (SSN) for individuals

Your Social Security Number is a nine-digit code assigned by the Social Security Administration when you are born or when you first become authorized to work in the United States. It is the tax number most people use. Your employer asks for your SSN on your W-4 form so they can report your wages to the IRS under your name and number. The IRS then matches that wage report to your tax return to make sure the income you reported is correct.

You also use your SSN to open bank accounts, apply for credit, and receive government benefits. If you were born in the U.S., you received an SSN automatically or your parents applied for one. If you were born outside the U.S. and later became authorized to work here, you can request an SSN from the Social Security Administration by showing proof of identity, age, and work authorization.

Employer Identification Number (EIN) for businesses

An Employer Identification Number is a nine-digit code the IRS assigns to a business, partnership, corporation, or nonprofit organization. If you are self-employed as a sole proprietor (you work for yourself and have no employees), you can use your Social Security Number on your tax return instead of an EIN. However, if you form a business structure like an LLC, S-corp, or C-corp, or if you hire employees, you must have an EIN.

You use your EIN to file business tax returns, open a business bank account, hire employees, and report payroll taxes. You can request an EIN from the IRS for free online, by phone, or by mail. The online application is instant — you receive your EIN immediately and can begin using it the same day. The IRS does not charge a fee for an EIN.

Individual Taxpayer Identification Number (ITIN) if you don't have an SSN

If you do not have a Social Security Number and are not authorized to work in the U.S., you may still be able to file taxes and work in certain situations by using an Individual Taxpayer Identification Number (ITIN). An ITIN is a nine-digit tax number the IRS issues to individuals who need to file a U.S. tax return but do not have an SSN. You might need an ITIN if you are a nonresident alien with U.S. income, a dependent or spouse of a U.S. citizen, or in some cases if you are undocumented but have earned income.

You request an ITIN by filing Form W-7 with the IRS and providing proof of identity and residency. The process takes several weeks. An ITIN allows you to file taxes and claim refunds, but it does not authorize you to work in the U.S. — work authorization is a separate legal status determined by immigration law, not tax law.

How the IRS uses your tax number

The IRS uses your tax number to create a file in their system that tracks all income reported under that number. When your employer files a W-2 form, they report your wages under your tax number. When a bank pays you interest, they report it under your tax number. When you file your own tax return, you use the same tax number. The IRS computer system matches the income reports to your return to verify that you reported all your income and that the amounts match.

If income is reported under your tax number but you did not report it on your return, the IRS will send you a notice asking you to explain the difference. If you reported income that was not reported by an employer or financial institution, you may be asked to provide documentation. This matching process is how the IRS detects unreported income and catches errors on tax returns.

What happens if you lose or forget your tax number

If you have lost your Social Security card or forgotten your number, you can request a replacement card from the Social Security Administration. You will need to show proof of identity, age, and citizenship or work authorization. The replacement card is free and usually arrives within two weeks. You do not need the physical card to use your number — you only need to know the nine digits. Many people never carry their Social Security card and simply remember the number.

If you have forgotten your EIN, you can look it up on prior tax returns, bank statements, or payroll records. You can also call the IRS at 1-800-829-4933 and provide your name and business information, and they will tell you your EIN. The IRS does not reissue EINs — each business keeps the same EIN for life, even if the business changes ownership or structure.

Tax number vs. other government ID numbers

Your tax number is different from other identification numbers you may have. Your driver's license number is issued by your state and is used for driving and identification purposes, not taxes. Your passport number is issued by the State Department for travel. Your state ID number for benefits like unemployment or food assistance is separate from your tax number. Some of these numbers may be linked in government databases, but they serve different purposes and are issued by different agencies.

The IRS only cares about your tax number — the SSN, EIN, or ITIN. When you file taxes or report income, you use your tax number, not your driver's license or passport. If you are applying for a government benefit and are asked for a tax number, they are asking for your SSN, EIN, or ITIN, not another form of ID.

Frequently Asked Questions

Can I have both an SSN and an EIN?

Yes. If you are self-employed or own a business, you can have both your Social Security Number and an Employer Identification Number. Many business owners use their SSN on their personal tax return and their EIN on their business tax return. Some use their EIN for business banking and payroll even if they are the only employee.

Do I need a tax number to work?

Yes. Your employer must have your tax number to report your wages to the IRS. If you do not have a Social Security Number, you can request one from the Social Security Administration, or you may be able to work using an ITIN in limited situations. Without a tax number, you cannot legally be hired for most jobs.

What if someone uses my tax number fraudulently?

If you believe your tax number has been used fraudulently, contact the IRS immediately at 1-800-908-4490 or file a report on the IRS website. You should also contact the Social Security Administration and place a fraud alert with the credit bureaus. The IRS has procedures to help victims of identity theft resolve tax-related fraud.

How long does a tax number last?

Your Social Security Number lasts your entire life. Your Employer Identification Number lasts as long as your business exists, even if you sell it or change its structure. You do not need to renew either number. If your business closes, the EIN is retired, but you can request a new one if you start another business.

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.