Social Security Numbers explained
What’s in an SSN?
Area numbers reflect the state where a number was assigned. Some states have a single area number; for instance, anyone born in Alaska has an SSN beginning 574. In other states, area numbers cycle between all numbers assigned to the state, after which the group number is incremented.
Group numbers follow an unusual order: odd numbers 01–09, even numbers 10–98, then even numbers 02–08 and odd numbers 11–99.
Serial numbers are assigned sequentially from 0001 to 9999 for each area number-group number combination.
How guessable is your SSN?
SSNs were never intended to be secure identifiers. Social Security cards had “Not For Identification” written on them as late as 1972.
If you were born in the US between 1988 and 2011, your Social Security number is probably less secure than you think. Even if it wasn’t exposed in a data breach, it can be predicted fairly accurately from the SSNs of people who were born around the same time as you who have since died, made public in the Death Master File (DMF).
We're only guessing the first five digits here, but in many cases the sixth digit is also predictable.
FAQ
My number is guessable — what can I do?
According to the SSA, not much. Even if your number is leaked, they won't issue you a new one unless your identity is actually stolen. You might consider freezing your credit to limit unauthorized use.
Since the first five digits provide so little security, it's important to treat the last four digits of your SSN as you would the full number.
Longer term, we should ask financial institutions to move away from SSNs as private identifiers, and perhaps pass legislation limiting their use.
My number is way off
It happens! Though the method used by this site correctly guesses the first 5 digits of most people's SSNs, it is less accurate for large states. Consider yourself lucky :)
Privacy
This site does not collect any information entered. All calculations and lookups are run locally on your device.
Sources
The predictability of SSNs is best described in Predicting Social Security numbers from public data, and this site makes heavy use of its methodology and insights.
CGPGrey made a video explaining the history and quirks of SSNs that first brought their issues to my awareness.
The SSA explains the historical numbering scheme, the group order, and what changed in 2011.
Or start from the number
Have a number and want to know what it says? The reverse lookup shows the state that issued it and estimates when its holder was born.