SSN Structure
The breakdown and the group or serial reservation notes.
Example: reading one number block by block
Take 521-45-6789. 521 is the area (three digits). 45 is the group (two digits). 6789 is the serial (four digits). Hyphens are only punctuation; the tool strips them before it splits. If the area appears on the pre-2011 chart, you may see a historic note on the result. If the card was assigned on or after 25 June 2011, the same split is still useful for teaching, but the blocks no longer point to a state.
Which tool to use
This page splits AAA-GG-SSSS. The other tools answer different questions.
SSN Validator
Possible, impossible, sample, or ITIN class for one number.
SSN Area Numbers
Historic state or program band for the first three digits, and only before 25 June 2011.
Three blocks, one number
SSA still prints AAA-GG-SSSS. Hyphens are conventional. 123456789 and 123-45-6789 are the same nine digits.
AAA
Area
First three digits. Before 25 June 2011 the area came from SSA’s public allocation chart (state, territory, or historic program band), chosen from the issuing office or mailing ZIP, not birthplace. After randomization it does not mean a state.
GG
Group
Middle two digits, 01–99. Offices once opened groups in an odd-then-even ledger order. Group 00 was never assigned.
SSSS
Serial
Last four digits, 0001–9999 inside a group. They do not encode age, sex, or citizenship. Serial 0000 was never assigned.
Patterns that are never assigned
These reservation rules still apply after randomization. Area 333 and areas above 772 are not reserved. Claims that 734–749 or 773+ were never issued are outdated. See SSN Area Numbers.
| Pattern | Rule | Note |
|---|---|---|
| 000 | Area never assigned | Still closed after randomization |
| 666 | Area never assigned | Never assigned; still closed after 2011 |
| 900–999 | Cannot be an SSN | IRS ITIN / ATIN territory, not SSA |
| Group 00 | Never assigned | Still unused after 25 June 2011 |
| Serial 0000 | Never assigned | Still unused after 25 June 2011 |
How the area used to be chosen
Before 25 June 2011 the area came from SSA’s public allocation chart, chosen from the issuing office or the mailing ZIP on the application, not birthplace. The chart lives on SSN Area Numbers. The longer essay is What AAA-GG-SSSS used to mean.
How groups used to be opened
Groups were not issued in ordinary counting order. SSA’s administrative sequence, from POMS RM 10201.030, was:
- Odd groups 01–09
- Even groups 10–98
- Even groups 02–08
- Odd groups 11–99
That order is teaching only. It is not a way to recover a birth year. The High Group List that employers once used is frozen. It cannot say whether a modern card “has been issued.”
What changed on 25 June 2011
SSA randomized new assignments so unused areas (except 000, 666, and 900–999) could be given out nationwide. New numbers do not advertise a state. Cards issued before that date were not rewritten.
What the number does not tell you
Even a clean split into area, group, and serial is not a biography.
| Claim | Fact |
|---|---|
| Birth state | The area followed an office or a mailing ZIP, and only before 25 June 2011 |
| Age or birth year | Serial and group are administrative. They are not a date of birth |
| Sex or citizenship | SSA does not encode those facts in the nine digits |
| That the number was issued | Structure can only apply reservation rules. Issuance is a Numident question |
Official structure text is in POMS RM 10201.030 and the SSA history numbering scheme. The longer essay is the What AAA-GG-SSSS used to mean.
Reviewed 21 September 2026 against current SSA publications.
Frequently Asked Questions
What is AAA-GG-SSSS?
Nine digits: a three-digit area, a two-digit group, and a four-digit serial. Hyphens are conventional. 123456789 and 123-45-6789 are the same number.
What do the numbers in an SSN mean today?
For cards assigned on or after 25 June 2011, SSA says the old area-group-serial meaning is no longer significant. New numbers are assigned randomly.
Do the first three digits show where I was born?
No. Before 25 June 2011 they reflected the state where the application was filed or, after about 1972, the mailing ZIP on the original application, not a sure birthplace or current home.
What is the group number?
Historically an administrative block from 01 to 99. SSA opened groups in four waves: odd 01–09, even 10–98, even 02–08, then odd 11–99. Two people from the same era can have very different middle digits. It was never a personal code. Group 00 is not assigned. After randomization the wave order is history only.
What is the serial number?
Historically 0001–9999 inside a group. Serial 0000 is not assigned. It does not encode age, sex, or citizenship.
Are SSNs still assigned by state?
No. Randomization removed state allocation of area numbers for new cards. The Area Numbers page is a historic chart only.
Can I still use the High Group List?
Only as history of groups issued before 25 June 2011. SSA froze the list. It cannot say whether a randomized-era number has been issued.
Which patterns are impossible?
Area 000, 666, and 900–999; group 00; serial 0000. Outdated claims such as area 333 or “773 and above” are in the impossible-patterns guide.
Is this a lookup of who holds the number?
No. SSA does not publish a public who-holds-this-number list, and we do not run people search.
Do you generate unused SSNs from this structure?
No. Randomization exists in part so the first five digits cannot be guessed from a state and year.