Social Security Number Format — How SSNs Work in the United States

A Social Security Number (SSN) is a nine-digit number issued by the Social Security Administration (SSA) to US citizens, permanent residents, and eligible temporary residents. Originally created in 1936 to track individual earnings for Social Security benefits, the SSN has become the de facto national identification number used for taxes, credit, employment, and government services.

SSN Structure: AAA-GG-SSSS

Every Social Security Number follows the format AAA-GG-SSSS — nine digits separated into three groups by hyphens:

Area Number History

Pre-2011: Geographic Assignment

From 1936 to June 25, 2011, the first three digits (area number) were assigned based on the state where the SSN application was filed. The SSA divided area numbers among states, with more populous states receiving larger ranges.

Some notable area number assignments:

This geographic system meant that someone's state of origin (at the time of SSN application, usually birth) could be inferred from the first three digits. This was a known privacy weakness.

Post-2011: Randomized Assignment

On June 25, 2011, the SSA implemented SSN Randomization. Under this system:

• Area numbers are no longer assigned by geographic region
• Group numbers are no longer assigned in the old non-sequential pattern
• All nine digits are effectively randomized (within the valid ranges)
• The change was made to extend the lifespan of the numbering system and improve identity protection

SSNs issued before June 25, 2011 still follow the old geographic pattern. Only new SSNs are randomized.

Group Numbers Explained

The middle two digits (group number, 01-99) were historically assigned in a specific non-sequential order within each area number. The assignment followed this pattern:

1. Odd numbers from 01 to 09
2. Even numbers from 10 to 98
3. Even numbers from 02 to 08
4. Odd numbers from 11 to 99

This unusual assignment order was designed to facilitate manual filing systems in the 1930s. It allowed SSA clerks to organize cards efficiently in physical filing cabinets. The group number 00 was never assigned — it serves as a marker for invalid SSNs.

Serial Numbers

The last four digits (serial number) were assigned sequentially from 0001 to 9999 within each area-group combination. The number 0000 was never assigned.

This means that within a given area and group, up to 9,999 SSNs could be issued. The "last four" of an SSN are the digits most commonly used for identity verification (last 4 of SSN), which is ironic given that they were the most predictable part of the pre-2011 system.

Invalid SSN Ranges

The Social Security Administration has permanently reserved certain number combinations that will never be assigned to individuals:

The Woolworth Wallet Incident

In 1938, a wallet manufacturer named E.H. Ferree included a sample Social Security card in wallets sold at Woolworth department stores across the country. The card displayed the SSN 078-05-1120, which was actually the real SSN of Ferree's secretary, Hilda Schrader Whitcher.

Over the next several decades, more than 40,000 people reported using this number as their own SSN. At its peak in 1943, 5,755 people were simultaneously using Whitcher's SSN. The SSA voided the number permanently, and Mrs. Whitcher was issued a new SSN.

This incident remains one of the most cited examples of why SSNs should never be printed on documents or used as general identification numbers — a lesson that society has largely failed to learn.

How to Protect Your SSN

Your SSN is the single most valuable piece of personal data you have. If compromised, it can be used for identity theft, tax fraud, employment fraud, and more. Here is how to protect it:

• Never carry your Social Security card — store it in a secure location at home (safe, lockbox). You almost never need the physical card
• Question every request for your SSN — ask if an alternative identifier is acceptable. Many businesses request it out of habit, not legal necessity
• Never share your SSN via email, text, or phone — legitimate organizations will not ask for your full SSN through these channels
• Monitor your credit reports — use AnnualCreditReport.com to check for unauthorized accounts opened in your name
• Consider a credit freeze — a freeze prevents anyone (including you) from opening new credit accounts until you lift it. It is free and highly effective
• File your taxes early — tax identity theft involves criminals filing a fraudulent return using your SSN before you do
• Shred documents that contain your SSN before discarding them

What to Do if Your SSN is Stolen

If you believe your SSN has been compromised, take these steps immediately:

1. Place a fraud alert — contact any one of the three credit bureaus (Equifax, Experian, or TransUnion). They are required to notify the other two
2. Freeze your credit — contact all three bureaus individually to place a credit freeze. This is free under federal law
3. Report to the FTC — file a report at IdentityTheft.gov. You will receive a personalized recovery plan
4. File a police report — this creates an official record you may need for disputes with creditors
5. Review your credit reports — look for accounts, inquiries, and addresses you do not recognize
6. Contact the SSA — in extreme cases, you can request a new SSN, though this is rare and comes with significant complications
7. Monitor your accounts — watch for unauthorized transactions, unfamiliar medical bills, and unexpected tax notices

Frequently Asked Questions