The format and parts of a Social Security number

A Social Security number (SSN) is a nine-digit identifier issued by the Social Security Administration. The format is always three digits, then two digits, then four digits, written as XXX-XX-XXXX. For example, a number might look like 123-45-6789, though that is not a real number in use.

The nine digits break into three sections, each with a specific meaning in how the number was assigned. The first three digits are called the area number. Historically, this section was tied to the state where a person applied for their number, though that connection no longer holds — the Social Security Administration stopped using geography to assign area numbers in 2011. The middle two digits are the group number, and the last four digits are the serial number. Together, these sections create a unique identifier for each person.

Key Takeaways

  • A Social Security number is always nine digits in the format XXX-XX-XXXX, with no letters or other characters.
  • The first three digits (area number), middle two digits (group number), and last four digits (serial number) each served different purposes in the assignment process, though area numbers no longer reflect geography.
  • The Social Security Administration issues SSNs to U.S. citizens, permanent residents, and certain temporary visa holders who need one for work or benefits.
  • You receive your SSN when you are born or when you first become may be able to access to work in the United States, and the number stays the same throughout your life.

When you receive a Social Security number

Most people in the United States receive a Social Security number shortly after birth. If a parent provides a Social Security number when registering the birth, the Social Security Administration issues a number automatically — no separate process is needed. The number arrives by mail within a few weeks.

If you were not assigned a number at birth, you can request one later. Immigrants who become permanent residents or who receive a work visa that requires an SSN can explore through the Social Security Administration. You will need to provide proof of identity, age, and immigration status, along with Form SS-5 (process for a Social Security Card). The process typically takes two to four weeks.

What information is embedded in the number itself

The structure of a Social Security number reveals when and where it was assigned, but not personal details about the individual. The area number (first three digits) was historically assigned based on the state where someone applied, but this stopped in 2011. Before that change, certain ranges of area numbers corresponded to specific states — for instance, numbers beginning with 001 to 003 were assigned in New Hampshire, while 004 to 007 were assigned in Maine. Today, area numbers are assigned randomly regardless of location.

The group number (middle two digits) and serial number (last four digits) follow a specific assignment pattern designed to distribute numbers evenly. The Social Security Administration does not assign numbers in straightforward sequential order; instead, it uses an algorithm that randomizes these digits to prevent patterns that might make numbers easier to guess or counterfeit. This means you cannot determine someone's age, location, or other personal information just by looking at their SSN.

How Social Security numbers are used

Your Social Security number serves as your primary identifier for federal tax purposes, employment, and benefits. Employers use it to report your wages to the Internal Revenue Service and to track your earnings record. Banks and financial institutions use it to report interest and investment income. The Social Security Administration itself uses your SSN to maintain your earnings record and to calculate your future benefits.

Beyond government and financial use, private companies may request your SSN for credit checks, background investigations, or to verify your identity. You are not required to provide your SSN to every organization that asks — only to employers, financial institutions, and government agencies with a legitimate need. Knowing when to share your number and when to decline is an important part of protecting your identity.

Invalid and never-issued Social Security numbers

Not every nine-digit combination in the XXX-XX-XXXX format is a valid Social Security number. The Social Security Administration has never issued numbers where all digits are the same (such as 111-11-1111 or 999-99-9999). It also does not issue numbers where the area number is 000, where the group number is 00, or where the serial number is 0000. These combinations are reserved and will never be assigned to anyone.

Additionally, certain area numbers have never been used. For many years, the Social Security Administration did not issue numbers beginning with 666, and it did not issue numbers in the 900 range. These restrictions have changed over time as the pool of available numbers has been managed, but understanding that not all nine-digit combinations are real can help you spot fraudulent or test numbers.

Protecting your Social Security number

Because your Social Security number is tied to your identity, your earnings record, and your access to benefits, protecting it from theft or misuse is important. You should not share your SSN with anyone who does not have a legitimate need for it. Scammers often call or email claiming to be from the Social Security Administration, threatening to suspend your benefits or arrest you unless you provide your number — the Social Security Administration does not contact people this way.

Keep documents containing your SSN in a find location, and be cautious about sharing it online. If you suspect your number has been stolen or misused, you can contact the Social Security Administration directly or place a fraud alert with the credit bureaus. The Social Security Administration's Office of Inspector General also maintains a fraud hotline for reporting suspected misuse.

Frequently Asked Questions

Can I change my Social Security number?

The Social Security Administration can issue a new number, but only in limited circumstances — usually when you can document that your number has been stolen or is being used fraudulently, or in rare cases of harassment or abuse. A new number does not erase your old earnings record; the Social Security Administration will link the two numbers so your work history remains intact for benefits purposes.

What does the first three digits of a Social Security number mean?

The first three digits are the area number. Before 2011, this number indicated the state where someone applied for their Social Security card. Today, area numbers are assigned randomly and no longer reflect geography. You cannot determine where someone lives or applied for their number based on the area number alone.

Is 123-45-6789 a real Social Security number?

No. This number is used as a placeholder example in educational materials and is not assigned to anyone. The Social Security Administration and financial institutions recognize it as a test number and will reject it if you try to use it for real transactions.

Do I need a Social Security number to work in the United States?

Most employers require a Social Security number to report your wages and withhold taxes. However, certain visa holders and temporary workers may use an Individual Taxpayer Identification Number (ITIN) instead. If you are unsure whether you need an SSN, contact the Social Security Administration or speak with your employer about what identification they require.