How Unique are the Last 4 Digits of a Social Security Number (SSN)?

Many people believe that their social security number is unique just to them, but is this the truth? The answer is a surprising no, your social security number is not that  unique. The only unique part of it is the first five numbers. The last four digits are often used multiple times between many different people. It is said that out of 119 people, there is a 50%  chance that two people will have the same last four digits.

This percentage rises the more people that is taken into consideration. Out of 180 people, the percentage rises to 80%, and out of 300 people, it rises to a whapping 99% probability that two of them will have the same number. This is because our social security number is based off of our date of birth. When you consider all dates of birth over a range of 100yrs then there are 36,525 possible birth dates. That mean there are that if there is 10,000 people then the chance of any two of them having the same Date of Birth is > 0.99. The same thing happen with social security numbers.


One thought on “How Unique are the Last 4 Digits of a Social Security Number (SSN)?”

  1. This is surprising. I always thought the last four numbers of the social security assigned to only one person, because the last four numbers are the ones that are used the most to verify the person. So i would assume at least the last four digits would be different.

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