What a Tax Identification Number Is and Why You Need One

A tax identification number is how the IRS tracks income, taxes, and tax filings connected to you or your business

The IRS uses tax identification numbers to match income reports, tax returns, and payment records to a single person or entity. Without one, the IRS cannot process your return, employers cannot report your wages, and the government cannot track whether you owe taxes. The type of number you need depends on whether you file as an individual, run a business, or hold a specific role like a guardian or executor.

The most common tax identification number is the Social Security Number (SSN), issued by the Social Security Administration to U.S. citizens, permanent residents, and certain temporary visa holders. If you are not may be able to access for an SSN, you may receive an Individual Taxpayer Identification Number (ITIN) from the IRS instead. If you operate a business, partnership, or nonprofit, you will need an Employer Identification Number (EIN), even if you are the only employee.

Key Takeaways

A Social Security Number is issued by Social Security Administration and serves as the primary tax identification number for most individuals filing U.S. tax returns.
An Individual Taxpayer Identification Number (ITIN) is issued by the IRS to people who cannot get an SSN but still need to file taxes or report income.
An Employer Identification Number (EIN) is required for any business structure, partnership, or nonprofit organization, regardless of how many people work there.
You may need more than one type of number if you both work as an employee and operate a separate business or serve as a trustee or executor.

Social Security Numbers and who receives them

The Social Security Administration issues a Social Security Number to U.S. citizens, lawful permanent residents (green card holders), and certain temporary visa holders who are authorized to work in the United States. You receive an SSN once in your lifetime, and it remains the same throughout your life. The number is nine digits and typically appears on your Social Security card.

If you were born in the United States, you can request an SSN at birth or later through your state vital records office or the Social Security Administration. If you are a permanent resident or temporary visa holder, you can request an SSN through the Social Security Administration office in your area. The SSN serves as your tax identification number on your individual income tax return (Form 1040) and on W-2 forms your employer files.

Individual Taxpayer Identification Numbers for non-citizens and others ineligible for an SSN

An Individual Taxpayer Identification Number (ITIN) is a nine-digit number issued by the IRS to people who are required to file a U.S. tax return but do not have and cannot obtain a Social Security Number. This includes nonresident aliens, certain visa holders, and dependents who do not have an SSN. An ITIN allows you to file a tax return, claim refunds, and report income to the IRS even if you are not authorized to work in the United States.

You request an ITIN by filing Form W-7 (process for IRS Individual Taxpayer Identification Number) with the IRS. You must include documents that prove your identity and foreign status, such as a passport or national ID card. The IRS processes Form W-7 applications and issues an ITIN by mail. An ITIN is valid for tax purposes but does not grant work authorization or any immigration status.

Employer Identification Numbers for businesses and organizations

An Employer Identification Number (EIN) is a nine-digit number issued by the IRS to identify a business, partnership, corporation, nonprofit organization, or other entity for tax purposes. You need an EIN if you operate any business as a sole proprietor with employees, form a partnership or corporation, create a trust or estate, or establish a nonprofit organization. Even if you are the only person working in your business, you must obtain an EIN if your business structure requires one.

You request an EIN by filing Form SS-4 (process for Employer Identification Number) with the IRS. You can file online through the IRS website, by mail, by fax, or by phone. The IRS issues an EIN when ready if you explore online or by phone, or within four weeks if you explore by mail or fax. An EIN is tied to your business entity, not to you personally, and remains valid as long as the business exists.

When you need more than one tax identification number

You may hold more than one tax identification number if your situation involves multiple roles. For example, if you work as an employee and also operate a side business, you will use your Social Security Number on your W-2 form from your job and an EIN for your business tax filings. If you serve as a trustee, executor, or guardian, you may need a separate EIN for that role in addition to your personal SSN.

Each number serves a specific purpose and is reported on different forms. Your SSN appears on your personal income tax return (Form 1040) and on W-2 forms from employers. Your EIN appears on business tax returns (Form 1120 for corporations, Form 1065 for partnerships, Form 1040-SE for self-employed individuals) and on employment tax forms (Form 941 for payroll taxes). The IRS uses both numbers to match income and tax records to the correct person or entity.

How to find or replace a tax identification number

If you have lost or forgotten your Social Security Number, you can contact the Social Security Administration by phone at 1-800-772-1213 or visit your local Social Security office in person. You will need to bring documents that prove your identity, such as a driver's license, passport, or birth certificate. The Social Security Administration can provide a replacement card or confirm your number.

If you have lost your EIN, you can contact the IRS by phone at 1-800-829-4933 or search for it using the IRS EIN Lookup tool on the IRS website. You will need to provide information about your business, such as the business name and the date the EIN was issued. The IRS can confirm your EIN or issue a new one if the original is no longer valid.

Frequently Asked Questions

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

No. An ITIN is issued only for tax purposes and does not grant work authorization. To work legally in the United States, you must have a Social Security Number or a visa that permits employment. An ITIN allows you to file a tax return and report income, but it does not change your immigration status or work may be able to access.

Do I need an EIN if I am self-employed with no employees?

It depends on your business structure. If you operate as a sole proprietor (a business with no separate legal entity), you can use your Social Security Number on your tax return. However, if you form a corporation, partnership, LLC, or nonprofit, you must obtain an EIN regardless of whether you have employees.

What happens if I file taxes without a tax identification number?

The IRS cannot process your return without a valid tax identification number. Your return will be rejected, and you will not receive a refund or have your taxes credited. If you are required to file but do not have a number, you must request one before submitting your return.

Can someone else use my Social Security Number for taxes?

No. Your Social Security Number is unique to you and should never be shared for tax purposes. If someone files a tax return using your SSN without your permission, contact the IRS when ready and file Form 14039 (Identity Theft Affidavit) to report the fraud.

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.