A tax ID, short for tax identification number, is a unique number the federal government assigns to individuals, businesses, and other entities so the Internal Revenue Service can track income, process returns, and enforce tax laws. Federal law requires every person or organization that files a return, or appears on someone else’s return, to have one. Which type you need depends on who you are: a U.S. citizen or resident, a business or trust, a non-resident with a U.S. filing obligation, an adoptive parent, or a paid tax preparer.
The Five Types of Tax IDs
The IRS doesn’t issue a single, universal number. It uses five different kinds, and each one exists for a specific situation.
Social Security Number (SSN)
This is the most common tax ID. The Social Security Administration issues it to U.S. citizens, permanent residents, and certain authorized workers. For most individuals, the SSN serves as their tax ID on every return they file. It also links your lifetime earnings to Social Security and Medicare benefits.
Employer Identification Number (EIN)
An EIN is a nine-digit number the IRS assigns to businesses, nonprofits, trusts, estates, and other entities that file their own returns. It’s the business equivalent of an SSN, and the IRS uses it to keep the entity’s tax accounts separate from the personal returns of its owners.1Internal Revenue Service. Understanding Your EIN Any organization applying for 501(c)(3) tax-exempt status needs an EIN before it can even submit that application.
An EIN is permanent. Once assigned, it’s never reused or reassigned, even if the business closes without ever filing a return.2Internal Revenue Service. Closing a Business
Individual Taxpayer Identification Number (ITIN)
If you have a federal tax filing obligation but aren’t eligible for an SSN — because you’re a non-resident alien, a foreign national’s spouse claiming treaty benefits, or a dependent without work authorization — the IRS issues an ITIN. It’s formatted like an SSN (nine digits, XXX-XX-XXXX) but always begins with 9, with specific middle-digit ranges that mark it as an ITIN rather than a Social Security Number.3Internal Revenue Service. About Form W-7, Application for IRS Individual Taxpayer Identification Number
An ITIN is strictly for federal tax purposes. It doesn’t authorize you to work in the U.S., doesn’t qualify you for Social Security benefits, and doesn’t change your immigration status.
Adoption Taxpayer Identification Number (ATIN)
When you’re in the middle of a domestic adoption and can’t yet obtain the child’s SSN, the IRS issues a temporary ATIN so you can claim the child as a dependent while the adoption is pending. To qualify, the child must be legally placed in your home by an authorized agency, and you must have made a reasonable attempt to get the child’s existing SSN without success. You apply using Form W-7A with a copy of your placement documentation.4Internal Revenue Service. Adoption Taxpayer Identification Number
Preparer Tax Identification Number (PTIN)
Anyone who prepares or helps prepare federal tax returns for pay must have a valid PTIN before touching a single return. The PTIN goes in the “Paid Preparer” section of every return the preparer works on, giving the IRS a way to track which professionals are filing what.5Internal Revenue Service. PTIN Requirements for Tax Return Preparers
When You’ll Be Asked for a Tax ID
Tax IDs show up throughout everyday financial life, not just at tax time. Common situations include:
- Opening a bank, brokerage, or investment account, where anti-money laundering rules require the institution to verify your identity.
- Starting a job or freelancing. Employers need your SSN to report wages on Form W-2. Payers of independent contractors need your tax ID to file Form 1099-NEC.6Internal Revenue Service. Forms and Associated Taxes for Independent Contractors
- Forming an LLC, corporation, partnership, or nonprofit, which requires an EIN so the entity can file its own returns and run payroll.
- Applying for a loan, where the lender pulls your credit using your SSN or ITIN.
- Administering an estate or trust. An estate generally needs its own EIN after the owner dies. Irrevocable trusts also need a separate EIN. A revocable trust typically uses the grantor’s SSN during the grantor’s lifetime, then needs its own EIN once the grantor dies.7Internal Revenue Service. Information for Executors
How to Get One
The application process depends on which number you need.
Getting an EIN
The fastest route is the IRS online application, available Monday through Friday, 7:00 a.m. to 10:00 p.m. Eastern Time. You’ll complete the electronic version of Form SS-4, providing the entity’s legal name, address, entity type, reason for applying, and the name and personal tax ID of the “responsible party” — the individual the IRS holds accountable for the entity’s tax obligations. If everything checks out, the system issues the EIN immediately.8Taxpayer Advocate Service. Getting an EIN
The application is free. If anyone charges you a fee, you’re dealing with a middleman. The IRS is explicit that you never have to pay for an EIN.9Internal Revenue Service. Get an Employer Identification Number
To use the online tool, your principal business must be in the United States or a U.S. territory, and the responsible party needs a valid SSN, ITIN, or EIN. The IRS limits issuance to one EIN per responsible party per day. If you can’t use the online system, you can fax or mail the paper Form SS-4.
Getting an ITIN
ITIN applications go through Form W-7, which you can mail to the IRS ITIN Operation in Austin, Texas, or submit in person at a Taxpayer Assistance Center. The simplest supporting document is a valid passport, which proves both identity and foreign status in one document. Without a passport, you’ll need two documents from the IRS’s approved list — one proving identity and one proving foreign status — and at least one must include a photograph.10Internal Revenue Service. ITIN Supporting Documents
Acceptable alternatives include a national ID card, a visa issued by the U.S. State Department, a foreign military ID, a civil birth certificate, or a foreign driver’s license, among others. Everything must be an original or a certified copy, and nothing can be expired at the time you submit.
Processing is slow. Outside peak season, expect about seven weeks. Between mid-January and the end of April, or from overseas, it stretches to nine to eleven weeks.11Internal Revenue Service. Instructions for Form W-7
What Happens If You Don’t Provide One
When you fail to furnish a correct tax ID to someone who needs it — an employer, a bank, a client — the IRS can impose a $50 penalty for each failure, up to $100,000 per calendar year. This amount is set by statute and doesn’t adjust for inflation.12Office of the Law Revision Counsel. 26 USC 6723 – Failure to Comply With Other Information Reporting Requirements13Internal Revenue Service. 20.1.7 Information Return Penalties
The bigger hit is backup withholding. If you don’t give a payer a correct tax ID, or the IRS tells the payer your number doesn’t match, the payer must withhold 24% of your payment and send it to the IRS. Backup withholding applies to interest, dividends, payment card transactions, and many other kinds of income.14Internal Revenue Service. 2026 Publication 15 You can eventually recover the withheld amount by claiming it as a credit on your return, but until then you’re out roughly a quarter of every affected payment. The statutory rate is tied to the fourth-lowest individual tax bracket, currently 24%.15Office of the Law Revision Counsel. 26 USC 3406 – Backup Withholding
ITINs Can Expire
EINs are permanent, but ITINs are not. Any ITIN not used on a federal tax return for three consecutive years expires on December 31 of that third year. All ITINs issued before 2013 have already expired regardless of use.16Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
If yours has expired, you must renew it before filing your next return. Renewal uses the same Form W-7 with the same identity documentation. Filing with an expired ITIN can delay your refund and make you ineligible for certain tax credits until the renewal goes through. If you haven’t used your ITIN in a few years, check its status before tax season.
Protecting Your Number
Tax-related identity theft happens when someone uses your SSN or ITIN to file a fraudulent return and claim your refund. For proactive protection, the IRS offers an Identity Protection PIN (IP PIN): a six-digit number that changes every year and must appear on your return. Even if a thief has your SSN, they can’t file without the current IP PIN. Anyone with an SSN or ITIN who can verify their identity is eligible to enroll. The easiest method is through your IRS Online Account. If your adjusted gross income is below $84,000 (or $168,000 for married filing jointly), you can also enroll by submitting Form 15227.17Internal Revenue Service. Frequently Asked Questions About the Identity Protection Personal Identification Number (IP PIN)
The IP PIN only covers individual returns (Forms 1040, 1040-NR, 1040-PR, 1040-SR, and 1040-SS), so it won’t protect a business EIN. For personal returns, it’s one of the most effective safeguards available, and it’s free.