What a Tax ID Number Is and Who Needs One

A Tax ID number is a nine-digit identifier the IRS uses to track your income and tax filings. If you are a U.S. citizen or resident alien with income, you need one. The IRS calls it an Individual Taxpayer Identification Number (ITIN) if you do not have a Social Security number, or an Employer Identification Number (EIN) if you are running a business or partnership.

Most people already have a Social Security number, which the IRS treats as a tax ID. If you do not have one and cannot get one, you can obtain an ITIN instead. If you own a business, hire employees, or file as a partnership or corporation, you need an EIN separate from your personal number.

The path you take depends on your situation: whether you are an individual without a Social Security number, a business owner, or someone filing taxes for the first time.

Key Takeaways

  • If you have a Social Security number, that is your tax ID — you do not need to request a separate one.
  • An ITIN is a nine-digit number for people without a Social Security number who need to file taxes or report income.
  • An EIN is required if you own a business, operate as a partnership, or hire employees, regardless of whether you have a Social Security number.
  • You can request an ITIN by mail using Form W-7, or in person at an IRS office or an authorized acceptance agent.
  • You can request an EIN online at irs.gov, by phone, fax, or mail, and receive it the same day if you explore online.

Getting an ITIN If You Do Not Have a Social Security Number

To obtain an ITIN, you file Form W-7 with the IRS. You can submit it by mail or in person. The form asks for your name, date of birth, address, and country of citizenship. You must also include original documents or certified copies that prove your identity and foreign status — a passport, national ID card, or birth certificate are the most common.

Mail your completed Form W-7 and documents to the IRS address listed on the form. Processing takes about four to six weeks. If you want faster service, you can visit an IRS office in person or go to an authorized acceptance agent — these are tax professionals, community organizations, and libraries that the IRS has trained to accept W-7 applications. The agent verifies your documents on the spot and sends them to the IRS, which still takes the same processing time but saves you a mail trip.

Once the IRS approves your ITIN, they mail it to you. You can then use it to file tax returns, open a bank account, or report income to employers. An ITIN does not give you work authorization or change your immigration status — it is only for tax purposes.

Getting an EIN for a Business or Partnership

An EIN is a nine-digit number that identifies your business to the IRS and other agencies. You need one if you hire employees, operate as a partnership or corporation, or file certain types of business tax returns. You do not need an EIN if you are a sole proprietor with no employees — you can use your Social Security number instead — but many business owners get one anyway to keep their personal and business finances separate.

The fastest way to get an EIN is online at irs.gov. Go to the IRS website, find the EIN process tool, and fill out the form with your business name, address, type of business, and reason for needing the EIN. The system issues your number when ready, and you can print a confirmation letter right away. You do not need to mail anything or wait.

If you cannot explore online, you can call the IRS at 1-800-829-4933 during business hours, fax Form SS-4 to the IRS fax number listed on the form, or mail the form. Phone and fax applications are processed the same day. Mail applications take about four weeks.

What Documents You Need

For an ITIN, you need proof of identity and proof of foreign status. Acceptable identity documents include a valid passport, national ID card, driver's license, or birth certificate. Proof of foreign status can be a passport, national ID, or visa. The IRS requires original documents or certified copies — photocopies alone are not accepted unless they are certified by the issuing agency.

For an EIN, you do not need to submit documents with your process. The IRS asks for information about your business — your name, address, type of business structure, and the reason you need the EIN — but you provide this on the form itself. If you explore online or by phone, you answer questions and receive your number without mailing anything.

Timeline and What Happens After You explore

If you explore for an ITIN by mail, expect four to six weeks for processing. If you use an authorized acceptance agent, the timeline is the same, but you avoid mailing documents yourself. The IRS sends your ITIN by mail to the address you provided on the form.

If you explore for an EIN online, you receive your number when ready and can print a confirmation letter. If you explore by phone, you get your number during the call. If you fax or mail Form SS-4, processing takes about four weeks, though some faxed applications are processed faster.

Once you have your number, write it down and keep it safe. You will need it every time you file a tax return, open a business bank account, or report income to an employer. The IRS does not send you a physical card — your number is issued once and stays the same for life.

If You Already Have a Social Security Number

If you are a U.S. citizen or resident alien and you have a Social Security number, that number is your tax ID. You do not need to request an ITIN or any other number. Use your Social Security number on all tax forms and when reporting income to employers.

If you are unsure whether you have a Social Security number, you can check by contacting the Social Security Administration at 1-800-772-1213 or visiting ssa.gov. They can tell you whether a number has been issued in your name.

Authorized Acceptance Agents for ITIN Applications

An authorized acceptance agent is a tax professional, community organization, or library that the IRS has trained to accept W-7 applications in person. Using an agent is optional — you can mail your process instead — but it saves time and gives you a chance to have your documents reviewed before they are sent to the IRS.

To find an agent near you, visit the IRS website and search for "acceptance agents" or call the IRS at 1-800-829-1040. They can tell you which agents are in your area and their hours. When you visit, bring your completed Form W-7 and original identity and foreign status documents. The agent verifies everything and sends it to the IRS on your behalf.

Frequently Asked Questions

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

No. An ITIN is only for tax purposes. It does not give you work authorization or change your immigration status. If you want to work legally in the United States, you need a separate work visa or employment authorization document from the Department of Homeland Security.

How long does an EIN last?

An EIN lasts for the life of your business. Once issued, it does not expire. If your business closes, you do not need to cancel the EIN — it straightforward becomes inactive. If you start a new business, you need a new EIN.

Can I get an ITIN if I am not a U.S. resident?

Yes. You can obtain an ITIN if you have U.S. income to report, even if you live outside the United States. You must still provide proof of identity and foreign status, and you can mail your process or use an authorized acceptance agent if one is available in your country.

What if I lose my ITIN or EIN?

If you lose your ITIN, contact the IRS at 1-800-829-1040 and they can look it up for you using your name and date of birth. If you lose your EIN, you can find it on previous tax returns or business documents, or call the IRS and provide your business name and address. The IRS does not reissue numbers — they straightforward confirm the one you already have.

Do I need an EIN if I am a sole proprietor with no employees?

No, you can use your Social Security number instead. However, many sole proprietors get an EIN anyway to keep their personal and business finances separate, which can make accounting and banking easier. Getting an EIN is optional for sole proprietors without employees.