SSN.lol: Social Security Numbers explained

What’s in an SSN?

Area numbers correspond to the state an SSN was assigned in. 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 count upwards each time the area numbers roll over, following an unusual but deterministic pattern.

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).

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 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 done 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.