What Your IRS Number Is and Why You Need It

Your IRS number is your unique identifier with the tax agency

The IRS uses several numbers to identify you, depending on your situation. Most commonly, this is your Social Security Number (SSN) — a nine-digit number issued by the Social Security Administration. If you do not have an SSN, the IRS issues an Individual Taxpayer Identification Number (ITIN), which looks like a Social Security Number but starts with 9. If you are filing as a business, you will use an Employer Identification Number (EIN) instead, which is nine digits in the format XX-XXXXXXX.

The IRS uses whichever number applies to you to match your tax return to your account, track payments, and link you to any refunds or notices. Without the correct number on your return, the IRS cannot process it, and you will not receive a refund or credit you are owed.

Key Takeaways

Your Social Security Number is your IRS number if you are a U.S. citizen or permanent resident; if you are not may be able to access for an SSN, you will need an ITIN instead.
An ITIN is a nine-digit number starting with 9 that the IRS issues to non-citizens who need to file taxes or claim credits.
Businesses and self-employed people file under an Employer Identification Number (EIN), not a personal number.
The IRS uses your number to match your return to your account, process refunds, and send notices about taxes you owe or credits you may receive.

Social Security Number as your primary IRS identifier

If you are a U.S. citizen, permanent resident, or authorized to work in the United States, you have a Social Security Number. This is the number the IRS expects on your tax return. It appears on your Social Security card and in your Social Security account records.

When you file a tax return, you enter your SSN in the box labeled "Your social security number" on Form 1040 or whichever form you use. The IRS matches this number to your name and address to pull up your account. If the number does not match the name on your return, the IRS will reject the return and send you a notice asking you to correct it.

You can find your SSN on your Social Security card, your tax returns from prior years, or your W-2 forms from employers. If you have lost your card or do not remember your number, you can contact the Social Security Administration at 1-800-772-1213 or visit ssa.gov to request a replacement card.

Individual Taxpayer Identification Number (ITIN) if you do not have an SSN

An ITIN is a tax identification number the IRS issues to people who are not may be able to access for a Social Security Number but need to file a U.S. tax return or claim a tax credit. ITINs are nine digits long and always begin with 9 in the fifth and sixth positions (for example, 9XX-XX-XXXX).

You may need an ITIN if you are a nonresident alien, a resident alien without an SSN, or a dependent or spouse of a U.S. citizen or resident alien. You cannot use an ITIN to work legally in the United States — it is only for tax purposes.

To obtain an ITIN, you file Form W-7 (process for IRS Individual Taxpayer Identification Number) with the IRS. You must include proof of identity and proof of foreign status. You can mail the form and documents to the IRS address listed on the form, or you can explore in person at an IRS office or an authorized acceptance agent. Processing typically takes four to six weeks by mail.

Employer Identification Number (EIN) for businesses and self-employed filers

If you are self-employed or own a business, you may need an EIN in addition to or instead of using your Social Security Number on your tax return. An EIN is a nine-digit number in the format XX-XXXXXXX (for example, 12-3456789) issued by the IRS to identify your business entity.

You must have an EIN if your business is structured as a corporation, partnership, or LLC with multiple members. If you are a sole proprietor with no employees, you can use your Social Security Number on your Schedule C (self-employment income form), but many sole proprietors obtain an EIN anyway to keep their personal and business finances separate.

You can obtain an EIN for free by explore online at irs.gov/ein. The online process takes about 15 minutes and you receive your number when ready. You can also explore by phone, fax, or mail, though those methods take longer.

How the IRS uses your number to process your return

When you file your tax return, the IRS scans your number and matches it to the name and address on your return. The IRS then pulls up your account — a record of all income reported to them under that number, all payments you have made, and any prior returns you have filed.

The IRS compares the income and deductions on your return to what third parties (employers, banks, investment firms) have already reported to them under your number. If there are discrepancies, the IRS may send you a notice or hold your refund while they investigate. If everything matches, your return is processed and any refund is issued to the bank account or address you provided.

If you file with the wrong number or a number that does not match your name, the IRS cannot process your return. You will receive a notice asking you to file an amended return with the correct information. This delays your refund and can trigger penalties if you owe taxes.

What to do if you do not know your IRS number

If you need your Social Security Number, contact the Social Security Administration at 1-800-772-1213 or visit ssa.gov. You can also check prior tax returns, W-2 forms, or 1099 forms from employers or financial institutions.

If you need your ITIN, check any prior correspondence from the IRS or your prior tax returns. If you have lost it and cannot locate it, you can reapply using Form W-7.

If you need your EIN, check your business formation documents, prior business tax returns, or any correspondence from the IRS. You can also call the IRS at 1-800-829-4933 and provide your name and business information; they can look up your EIN for you.

Frequently Asked Questions

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

No. An ITIN is only for tax purposes. To work legally in the United States, you must have a Social Security Number or an Employment Authorization Document (EAD). An ITIN does not authorize you to work.

Do I need both an SSN and an EIN?

If you are self-employed or own a business, you may have both. You use your SSN on your personal tax return and your EIN on your business tax return. Many sole proprietors use only their SSN, but an EIN keeps your personal and business finances separate on IRS records.

What happens if I file with the wrong IRS number?

The IRS will reject your return and send you a notice asking you to file an amended return with the correct number. Your refund will be delayed until you correct it. If you owe taxes, penalties and interest may accrue while the error is being resolved.

How long does it take to get an ITIN?

By mail, processing takes four to six weeks. If you explore in person at an IRS office or authorized acceptance agent, you may receive your ITIN faster. Check irs.gov for a list of acceptance agents in your area.

Can I change my IRS number?

No. Your Social Security Number, ITIN, and EIN are permanent. If you believe your number has been compromised or used fraudulently, contact the IRS at 1-800-829-1040 or the Social Security Administration at 1-800-772-1213.

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.