What Is a Social Security Number (SSN)? Key Facts and Uses

By Markets & Investing DeskUpdated Nov 10, 2026

Definition

A Social Security number is a nine-digit number the Social Security Administration assigns to record a person's earnings and decide eligibility for Social Security benefits.

Key takeaways

Since June 25, 2011, new SSNs are assigned randomly and no longer reveal the state or issue order.
Getting a number or a card from the SSA is free, and replacements are capped at three per year and ten per lifetime.
An ITIN begins with 9 and serves tax reporting only, with no work authorization or benefit eligibility.
A credit freeze with Equifax, Experian and TransUnion is free and blocks most new credit opened in your name.

A Social Security number (SSN) is a nine-digit number that the U.S. Social Security Administration (SSA) assigns to an individual, under Section 205(c)(2) of the Social Security Act (42 U.S.C. § 405), to record that person’s earnings and determine eligibility for Social Security benefits. It is written as XXX-XX-XXXX. The number was created in 1936 to keep track of wages under the new Social Security program. It has since become the main identifier for federal taxes, credit reporting, banking and many government services. An SSN identifies one person for life. It is not proof of identity on its own, which makes it valuable to identity thieves.

The SSN is an account number for your record with the SSA. Each year your employer reports your wages under that number, and the SSA adds those earnings to your lifetime record. When you apply for retirement, disability or survivor benefits, the agency uses that record to decide whether you qualify and how much you receive.

Nearly all U.S. citizens and permanent residents have an SSN, as do many temporary residents authorized to work and people who need one for a government or business purpose. The SSA issues both the number and the card, which is simply a record of the number. Losing the card does not change or cancel the SSN.

An SSN is divided into three parts: a three-digit area number, a two-digit group number and a four-digit serial number. For most of the program’s history, each part had a specific meaning. That changed in 2011.

Area number (first three digits). Under the original system, the area number showed the state where the number was issued, and populous states received more than one. For example, 001 to 003 belonged to New Hampshire and 575 to 576 to Hawaii. Numbers rose from the Northeast toward the West, so East Coast numbers are generally lower than West Coast ones. Beginning in 1972, the area number was based on the ZIP code of the application’s mailing address, which was not necessarily where the applicant lived. Even older SSNs are therefore only a rough indicator of residence.

Several area numbers were set aside for special purposes:

700 to 728 were assigned to railroad employees until 1963.
586 went to American Samoa, Guam, the Philippines, Americans employed abroad by U.S. companies, and Indochinese refugees from 1975 to 1979.
729 to 733 were allocated to the Department of Homeland Security for its Enumeration at Entry program, which assigns numbers to noncitizens admitted for permanent residence.
666 has never been assigned and will not be.
000 has never been used, and numbers beginning with 9 are not issued as SSNs. The IRS uses that range for Individual Taxpayer Identification Numbers.

Group number (middle two digits). Group numbers run from 01 to 99; 00 is never used. They originally stood for blocks of 10,000 numbers distributed to the post offices that registered workers in each state, and later represented the issuing office. Groups were not filled in strict numerical order.

Serial number (last four digits). Within each group, serial numbers ran in order from 0001 to 9999. The serial number 0000 is never used.

Randomization in 2011

On June 25, 2011, the SSA switched to randomized assignment. New SSNs no longer reflect the applicant’s state, and the sequential order within groups was dropped. The agency had two main reasons for the change. First, some states were running low on available numbers under the old pattern. Second, a number whose first five digits could be inferred from a person’s birthplace and birth date was easier to guess. Randomization also freed many previously unassigned area numbers.

The SSA does not reuse numbers after a person dies. There have been rare cases where two people were mistakenly issued the same number. About 420 million numbers are available for assignment under the current system.

President Franklin D. Roosevelt signed the Social Security Act in 1935, creating benefits for workers age 65 and older based on their earnings before retirement. Paying those benefits required a way to track each worker’s wages across employers and years. The Social Security Board created the nine-digit number for that purpose, and the first numbers were issued in late 1936.

The SSN’s role expanded steadily over the following decades:

1943: An executive order directed federal agencies to use the SSN when they needed a numerical identifier for individuals.
1962: The Internal Revenue Service began using the SSN as the taxpayer identification number for individuals.
1970: Banks were required to obtain their customers’ SSNs.
1972: Area numbers began to be assigned by the ZIP code of the applicant’s mailing address.
1987: Enumeration at Birth allowed parents to request an SSN for a newborn as part of the birth registration process. Federal tax law around the same time began requiring SSNs for dependents claimed on returns.
2011: SSN assignment became randomized.

The SSA uses the earnings and years of covered work recorded under your number to determine eligibility for retirement income, disability benefits, survivor benefits and Medicare. Wages reported under the wrong number or a misspelled name may not appear in your record, which can reduce your benefits until the error is corrected.

When you start a job, your employer asks for your SSN. The employer then reports your wages and the Social Security and Medicare taxes withheld from your pay to the SSA and the Internal Revenue Service on Form W-2. Independent contractors provide their SSN or another taxpayer ID to clients on a Form W-9, so that payments can be reported under the correct number.

Beyond employment and taxes, you are typically asked for an SSN to:

Open a bank, brokerage or other account that earns interest or dividends
Apply for credit cards, mortgages, auto loans and federal student loans
File federal and state income tax returns, and claim dependents
Apply for unemployment benefits, Medicaid, SNAP and other public assistance
Enroll in Medicare and apply for Social Security benefits
Obtain a driver’s license in many states
Apply for a U.S. passport

Lenders and credit bureaus use the number to match accounts and payment histories to the correct person. This is why a credit report is effectively tied to an SSN rather than to a name alone.

Tip: Whether you must give your SSN depends on who is asking. Tax-related and benefit-related requests usually have a legal basis. A landlord, doctor’s office or retailer may ask for it but often cannot require it. You can ask whether another identifier will work instead.

To get a number, a replacement card or a corrected record, you file Form SS-5, Application for a Social Security Card, with the SSA. The same form covers all three requests.

Gather documents. You need original or agency-certified evidence of your age, identity, and U.S. citizenship or lawful immigration status, such as a birth certificate, U.S. passport, or Department of Homeland Security immigration documents.
Submit the application. Turn in the completed SS-5 and your documents to the SSA. Parents can usually request a newborn’s number at the hospital when they register the birth, and many noncitizens can request one during the immigration process.
Wait for the card. The SSA mails the card once it has verified everything, usually in two to four weeks, and longer during processing delays.

There is no charge for a number or a card. Be wary of any service that asks you to pay for one.

The SSA issues three types of cards. An unrestricted card goes to citizens and permanent residents. A card reading “valid for work only with DHS authorization” is issued to people with temporary work permission. A card marked “not valid for employment” goes to noncitizens who need a number for a non-work purpose, such as receiving certain benefits.

Replacement cards are limited to three per year and ten over a lifetime. Changes such as a legal name change or a correction of citizenship status do not count toward those limits. A name change after marriage or a court order requires an updated card, but your number stays the same.

If you do not know your SSN, look for it on your Social Security card, a Form W-2 or 1099, a past tax return, or SSA correspondence. Otherwise, request a replacement card from the SSA. The agency does not give out numbers over the phone to unverified callers, and third-party websites are not a safe source.

Hypothetical example for illustration only; the digits do not belong to any person.

Suppose two siblings have SSNs that begin 003-xx-xxxx and 75x-xx-xxxx.

The older sibling received a number before 2011 that starts with 003. That area number belonged to New Hampshire, so it was most likely issued through an address there. The middle digits would indicate the issuing office’s group, and the last four the order within that group.
The younger sibling received a number in 2015 that starts with 75x. Under the old pattern, the 700s mostly meant railroad workers or special programs. Under randomization, the number reveals nothing about the state, the office or the issue date.

A pre-2011 number can sometimes be traced to a place; a post-2011 number cannot. Either way, the number confirms only that the SSA assigned it, not that the person presenting it is the holder.

SSN vs. Other Identification Numbers

Several government numbers are easy to confuse with an SSN:

Taxpayer identification number (TIN). This is the umbrella term the IRS uses. For most individuals, their TIN is their SSN.
Individual Taxpayer Identification Number (ITIN). The IRS issues an ITIN to people who must file U.S. taxes but are not eligible for an SSN, such as some nonresident aliens. ITINs begin with 9. They are for tax reporting only and do not give work authorization or Social Security benefit eligibility.
Employer Identification Number (EIN). The IRS assigns an EIN to businesses, trusts, estates and other entities. It is formatted XX-XXXXXXX. A sole proprietor may use either an EIN or an SSN, depending on the situation.
Medicare Beneficiary Identifier (MBI). Medicare cards used to show an identifier based on the SSN. Between 2018 and 2019, these were replaced with a randomly generated MBI that has no link to the SSN.
Foreign equivalents. Other countries use their own numbers, such as Canada’s Social Insurance Number. These are not interchangeable with a U.S. SSN.

The SSN was designed to track earnings, not to prove identity. It has no photo, fingerprint or other biometric element, and the card has few security features compared with a passport or driver’s license. Yet many institutions treat knowledge of the number as proof of identity, and that gap is the root of most SSN fraud.

Other limitations follow from the design:

Permanence. A password can be changed after a breach. An SSN usually stays the same for life, so exposure in a data breach can create risk for years.
Wide distribution. Because so many employers, lenders, insurers and medical providers store SSNs, each one is a potential point of leakage.

The risk is not theoretical. In 1938, a wallet manufacturer placed sample cards in its wallets showing an employee’s real number, 078-05-1120. Thousands of buyers later used it as their own, and the SSA eventually voided it. More recently, the chief executive of an identity theft protection company published his own SSN in advertisements, and his identity was later stolen multiple times. Some legislators have proposed restricting SSN requests for everyday activities such as renting an apartment or buying a hunting or fishing license.

Important: An SSN is personally identifiable information. Under the Privacy Act of 1974, federal agencies that ask for it must tell you whether disclosure is mandatory or voluntary and on what legal authority they ask. Private businesses have fewer restrictions.

What someone can do with your SSN

A person who has your SSN, especially together with your name and date of birth, may be able to:

Open credit cards or loans in your name
Get a job using your number, which can cause wages to be reported under your record
File a fraudulent tax return and claim your refund
Receive medical treatment billed to you
Apply for government benefits in your name

How to tell whether your SSN is being misused

No single alert shows when an SSN is compromised, and misuse is often found only after damage occurs. Practical checks include:

Reviewing your credit reports from Equifax, Experian and TransUnion for accounts you did not open.
Comparing the earnings on your SSA record with your W-2s. Wages you never earned may mean someone is working under your number.
Requesting IRS tax transcripts, or responding promptly to any IRS notice about a duplicate return or unreported income.
Watching bank and medical statements for unfamiliar activity.

What to do if your SSN is stolen

If your card is lost or your number is being used by someone else:

Place a fraud alert or credit freeze with the three credit bureaus. A freeze blocks most new credit in your name and is free.
Report the identity theft at IdentityTheft.gov, the Federal Trade Commission’s recovery site, which generates a recovery plan.
Contact the SSA about misuse related to earnings or benefits, or to replace a lost card.
Notify the IRS if tax fraud is involved. It can issue an Identity Protection PIN, required to file a return under your SSN.
File a police report for an actual theft, and report online fraud to the FBI’s Internet Crime Complaint Center.
Contact your bank and lenders about any account opened or used without permission.

The SSA assigns a new SSN only in limited circumstances, such as for victims of domestic violence or harassment, people still harmed by misuse of their number after trying to resolve it, and cases where two people were given the same number. You must apply in person with evidence of the ongoing harm. A new number does not erase old credit or tax records, and lenders and agencies may link the two numbers, so the SSA does not issue one simply because a card was lost or a number appeared in a data breach.

The Bottom Line

Anyone who works, pays taxes, borrows or claims benefits in the U.S. relies on an accurate SSN record. Because the number usually stays the same for life and does not prove identity, the safest approach is to share it only when required and compare your SSA earnings record with your W-2s. Check your credit reports regularly, and if misuse appears, freeze your credit and report it at IdentityTheft.gov.