An identification or registration number (IRN) is a unique code a government agency or licensing body assigns to track you, your business, or your professional credentials. To find your IRN number, start with the original document the agency issued and any paperwork that used it afterward; if those are gone, every issuing agency has a retrieval process, and the right one depends on which number you’re trying to recover.
The sections below cover the numbers people most often need to track down, where each one is printed, and what to do if the paper trail is gone.
Social Security Number
Your Social Security number sits on your Social Security card and on virtually every federal tax return you’ve filed. On a past return, it’s printed near the top of the first page. It also appears on W-2 forms from employers and 1099 forms from banks or investment accounts.
If the card itself is gone, the Social Security Administration issues free replacements online, by phone, or in person. Some situations qualify for online replacement through the SSA’s website; others require an appointment at a local office.1Social Security Administration. Replace Social Security Card Replacement cards arrive by mail within 5 to 10 business days.
To prove identity, the SSA asks for an unexpired U.S. driver’s license, state-issued non-driver ID card, or U.S. passport. If you don’t have any of those, the agency will accept other documents showing your legal name along with identifying information such as your date of birth or a recent photograph, like an employee ID or school ID. All documents must be originals or certified copies from the issuing agency.2Social Security Administration. Application for Social Security Card
Employer Identification Number
An EIN is the federal tax ID the IRS assigns to businesses, nonprofits, trusts, and other entities. It’s printed on the confirmation notice the IRS mailed when you first applied, and on every business tax return you’ve filed. Your bank also has it on file for any business accounts you opened.
If none of those are within reach, the IRS suggests checking with state or local agencies where you applied for business licenses, since many of those applications required the EIN. When that fails, call the IRS Business and Specialty Tax Line at 800-829-4933, Monday through Friday, 7 a.m. to 7 p.m. local time. After verifying the caller’s identity, the IRS will provide the EIN over the phone.3Internal Revenue Service. Employer Identification Number
The same phone line can issue a Letter 147C, a written confirmation of your previously assigned EIN that banks, vendors, or government agencies often ask for as official proof. An entity transcript from the IRS also confirms the number.3Internal Revenue Service. Employer Identification Number
Individual Taxpayer Identification Number
An ITIN is a nine-digit number the IRS issues to people who need a U.S. taxpayer ID for federal tax purposes but aren’t eligible for a Social Security number, including certain nonresident aliens and their spouses and dependents who must file a U.S. tax return. An ITIN is not identification outside the federal tax system and doesn’t authorize work in the United States.4Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
Your ITIN appears on the CP565 notice the IRS mailed when the number was first assigned. When an ITIN application was submitted with a tax return, the IRS also wrote the assigned ITIN directly on that return before processing it, so old return copies are a reliable backup.
If both are gone, contact the IRS. From inside the United States, call the toll-free number listed on IRS correspondence. From outside the country, call 267-941-1000, which is not toll-free.5Internal Revenue Service. Understanding Your CP565 Notice
One detail catches people out: an ITIN expires if it isn’t used on a federal tax return for three consecutive tax years, with the expiration falling on December 31 after that third year. Filing with an expired ITIN can delay your return, block certain credits, and reduce your refund, so you’ll need to renew before filing.6Internal Revenue Service. How to Renew an ITIN
Alien Registration Number
The Alien Registration Number (A-Number) is a seven-, eight-, or nine-digit identifier the Department of Homeland Security assigns to noncitizens in the U.S. immigration system.7U.S. Citizenship and Immigration Services. A-Number/Alien Registration Number/Alien Number It appears on Permanent Resident Cards, Employment Authorization Documents, immigrant visa stamps, and USCIS notices.
On Permanent Resident Cards issued after May 10, 2010, it’s on the front of the card as the USCIS Number. On an immigrant visa stamp, it’s labeled “Registration Number.” It also shows up on the immigrant data summary and the USCIS Immigrant Fee handout. If the number has fewer than nine digits, most systems require you to pad it with a zero after the “A” and before the first digit. So A12345678 becomes A012345678.8U.S. Citizenship and Immigration Services. Immigrant Fee Payment: Tips on Finding Your A-Number and DOS Case ID
Driver’s License and State ID Numbers
Your driver’s license or state ID number is printed on the front of the card, usually near your photo or personal details. It’s easy to confuse with the issue date, expiration date, or document discriminator number some states also print on the card. The one you want is labeled “DL” or “ID No.” on most state formats.
For a lost card, contact your state’s Department of Motor Vehicles or equivalent agency. Most states allow an online replacement order if you can verify your identity with details like your date of birth, ZIP code, and the last four digits of your SSN. Some require an in-person visit when online verification fails. Replacement fees vary by state, generally $10 to $40, and the new card typically arrives by mail.
Professional Licenses and Business Permits
If you hold a professional license for medicine, law, engineering, contracting, or a similar field, or a local business permit, the number is printed on the original certificate. Look near the top or bottom for a label like “License No.,” “Permit ID,” or “Registration Number.”
When the certificate is lost, the retrieval path depends on the issuer. State licensing boards for professions like medicine or law often run free online lookup tools where you can search by name in a public directory. For local business permits, contact the city or county clerk’s office that issued it. Replacement certificates usually involve a modest fee and are often available through online portals.
Medicare, Provider, and Traveler Numbers
Medicare Beneficiary Identifier
Your Medicare Beneficiary Identifier (MBI) is the 11-character number printed on your Medicare card, replacing the old Social Security–based Health Insurance Claim Number. It’s a randomly generated mix of numbers and uppercase letters, formatted like 1EG4-TE5-MK73, with the dashes appearing on the card but not in electronic systems.9Centers for Medicare & Medicaid Services. Understanding the Medicare Beneficiary Identifier (MBI) Format If the card is lost, log in to your Medicare.gov account to view the number or call 1-800-MEDICARE for a replacement.
National Provider Identifier
Healthcare providers get a 10-digit National Provider Identifier for billing across the healthcare system. A provider who has misplaced an NPI can search the free NPPES NPI Registry by name, location, or taxonomy description.10U.S. Centers for Medicare & Medicaid Services. NPPES NPI Registry
Global Entry and Known Traveler Number
Your Trusted Traveler membership number, also called the PASS ID or Known Traveler Number, is printed on the back of your Global Entry card. It also appears at the top of the page after you sign in to your Trusted Traveler Programs account.11U.S. Customs and Border Protection. Where Can I Find My Trusted Traveler Membership Number
If Your Number Has Been Stolen
If you think your Social Security number has been compromised, the SSA directs you to the Federal Trade Commission rather than to Social Security itself. Go to IdentityTheft.gov, answer questions about your situation, and the site generates an Identity Theft Report along with a personalized recovery plan. You can also report by phone at 1-877-438-4338.12Social Security Administration. Report Stolen Social Security Number Keep that report; it’s official proof to businesses and creditors that someone stole your identity, and it triggers certain legal protections.
For a stolen EIN, call the IRS Business and Specialty Tax Line at 800-829-4933 to report the compromise. For immigration document theft, file a police report and contact USCIS. Speed matters. The longer a stolen number circulates, the harder cleanup gets.