The standard Social Security number format

A Social Security number (SSN) is a nine-digit identifier issued by the Social Security Administration. It follows a consistent format: three digits, then two digits, then four digits, written as XXX-XX-XXXX. For example, a number might look like 123-45-6789. The hyphens are part of the standard format, though some documents or systems may display the number without them.

Each of the three sections has a specific meaning. The first three digits are called the area number. The middle two digits are called the group number. The last four digits are called the serial number. Together, these nine digits create a unique identifier for each person who receives an SSN.

Key Takeaways

  • Social Security numbers follow the format XXX-XX-XXXX, with three sections that each carry different information about when and where the number was issued.
  • The first three digits (area number) historically indicated the state where the person applied for the number, though this is no longer strictly true after 2011.
  • The middle two digits (group number) have no geographic or personal meaning and are assigned in a specific sequence by the Social Security Administration.
  • The last four digits (serial number) are assigned sequentially and are the part that changes most frequently when new numbers are issued.
  • Certain number combinations are never issued — for example, numbers beginning with 000, 666, or 900-999 are not valid Social Security numbers.

What the area number (first three digits) tells you

Before 2011, the first three digits of a Social Security number indicated the state where the person applied for the number. Someone who applied in California would receive a number starting with 545 through 573. Someone who applied in New York would receive a number starting with 051 through 134. This made it possible to roughly determine where a number was issued by looking at the first three digits.

The Social Security Administration stopped using this geographic system in June 2011 and switched to random assignment. Today, the first three digits no longer indicate where someone lives or where they applied for their number. However, the old ranges are still documented, and some organizations use them to verify whether a number could have been issued to someone at a particular time in their life.

What the group number (middle two digits) means

The middle two digits of a Social Security number are assigned in a specific order by the Social Security Administration, but they do not represent any personal information about the holder. They are not tied to age, gender, employment status, or any other characteristic. The group number is simply part of the randomization system that ensures each SSN is unique.

The group numbers are assigned in a non-sequential pattern — they do not go from 01 to 99 in order. Instead, the Social Security Administration uses a predetermined sequence that was designed to distribute numbers evenly across the population. This sequence is public information and is documented on the Social Security Administration website.

What the serial number (last four digits) tells you

The last four digits of a Social Security number are the serial number. These digits are assigned sequentially, meaning they run from 0001 to 9999. The serial number is the part that changes most often when new numbers are issued. Once a number is assigned to a person, the serial number stays with them for life.

The serial number itself does not encode information about when the number was issued or in what order. It is simply a way to create the final unique identifier. Combined with the area number and group number, the serial number ensures that no two people receive the same nine-digit combination.

Numbers that are never issued

The Social Security Administration does not issue numbers with certain combinations of digits. Numbers that begin with 000 are never issued. Numbers that begin with 666 are never issued. Numbers that begin with 900 through 999 are never issued. Additionally, numbers where all four serial digits are 0000 (such as 123-45-0000) are never issued.

These restrictions exist for administrative and historical reasons. The 000 prefix was reserved for internal use. The 666 prefix was never assigned to any individual. The 900-999 range is used for other purposes, such as Individual Taxpayer Identification Numbers (ITINs) issued to non-citizens. If you encounter a number with any of these combinations, it is not a valid Social Security number.

How to read and verify the format

When you see a Social Security number written down, check that it follows the XXX-XX-XXXX pattern. Each X should be a single digit from 0 to 9. The hyphens should appear after the third digit and after the fifth digit. Some systems display SSNs without hyphens (for example, 123456789), but the underlying format remains the same.

If you need to verify that a number is formatted correctly, check that it has exactly nine digits, that none of the restricted combinations appear at the beginning, and that it is not all zeros or all the same digit. A correctly formatted number will have variation across all nine positions. If a number looks unusual — for example, if it has repeating patterns like 111-11-1111 — it may not be a valid number, though the only way to confirm validity is through official Social Security Administration records.

Why format matters in documents and applications

The standard format XXX-XX-XXXX is used on official documents like Social Security cards, tax forms, and government records. When you provide your Social Security number to an employer, bank, or government agency, they expect it in this format or without hyphens. Some computer systems automatically add or remove hyphens when processing the number.

If you are filling out a form and it asks for your Social Security number, check whether the form wants hyphens or not. Most modern online forms accept either format and convert it automatically. On paper forms, follow the instructions provided. If the form shows a template like _ _ _ - _ _ - _ _ _ _, use hyphens. If it shows a single blank line, write the nine digits without hyphens.

Frequently Asked Questions

Can you tell where someone lives by looking at their Social Security number?

Not reliably. Before 2011, the first three digits indicated the state where someone applied for their number, but this has not been true for numbers issued since June 2011. Even for older numbers, the area number only shows where the person applied, not where they currently live or where they were born.

What do the hyphens in a Social Security number mean?

The hyphens are formatting only — they separate the three sections for readability but do not carry any meaning themselves. The first hyphen comes after the third digit, and the second comes after the fifth digit. Some systems display the number without hyphens, and the number is still valid.

Is a Social Security number with repeating digits like 111-11-1111 valid?

No. The Social Security Administration does not issue numbers where all digits are the same. Numbers like 111-11-1111, 222-22-2222, or 000-00-0000 are not valid. If you encounter such a number, it is either a placeholder, an error, or a fraudulent number.

Can you change the format of your Social Security number?

No. Your Social Security number is fixed for life once it is issued. The format XXX-XX-XXXX is the standard way to write it, but the underlying nine digits never change. You cannot request a different number or a different format, though some systems may display it differently for security reasons.

Why does the Social Security Administration use this specific format?

The format was chosen to organize and track millions of numbers efficiently. The three sections allow the Social Security Administration to manage the assignment process and ensure uniqueness. The format has remained consistent since Social Security numbers were first issued in 1936, making it a standard that employers, banks, and government agencies all recognize.