How Are Social Security Numbers Assigned? All About the 9-Digit Number

Social Security numbers have become de facto national identification numbers used for many purposes. How are Social Security numbers assigned?

Anuradha Garg - Author

Dec. 14 2021, Published 1:38 p.m. ET

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Source: Social Security Administration Facebook

The SSA (Social Security Administration) issues the nine-digit SSN (social security number) to U.S. citizens, permanent residents, and temporary residents. The SSA is an independent agency of the U.S. government. SSNs started as a way for the SSA to track individuals. Now, the numbers have become a form of national identification used for many purposes, including taxation. The numbers are also used for tracking individuals’ lifetime earnings, tracking the number of years they have worked, and calculating social security benefits.

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The SSA issues three types of social security cards depending on your working status. While all three cards carry your name and SSN, the work status differs.

What are the three types of Social Security cards?

The three types of cards are:

  • The first card lets you work only without restriction - It's issued to U.S. citizens and people lawfully admitted to the U.S. on a permanent basis.
  • The second card lets you work only with DHS (Department of Homeland Security) authorization - It's issued to people lawfully admitted to the U.S. on a temporary basis who have DHS authorization to work.
  • The third card doesn't let you work - It's issued to people who are lawfully admitted to the U.S. without work authorization from DHS.
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social security numbers and cards
Source: SSA Twitter

SSNs are assigned through randomization.

SSNs are assigned through a process called randomization, which was introduced in June 2011. The method did away with the methods that were used to assign numbers since the mid-1930s. On July 3, 2007, the SSA published its intent to randomize the nine-digit SSN in the Federal Register Notice.

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Before this switch, the first set of three digits in the SSN was an area number. The codes were assigned to each state. The second set of two digits was called the group number, which divided numbers into blocks within those geographic areas. The final four-digit serial number individualized each full number within that block.

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What does the randomization method entail for Social Security numbers?

While the previously followed method was adopted at the time of manual bookkeeping, randomization is more suited to the digital age. Randomization serves two main purposes:

  • Randomization makes it difficult for identity thieves to reconstruct numbers using peoples’ publicly available information.
  • The method also extends the longevity of the numbers. The previous method limited the range of numbers that could be issued in a given state. Currently, there are about 420 million numbers available for assignment.
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Due to the new method of assigning SSNs, no existing Social Security numbers were replaced. The new system only impacts numbers issued since it was put in place. Another thing to keep in mind is that randomization will apply if you get a new Social Security number to replace a number assigned before the switch. However, Social Security only grants requests to change a number under very limited circumstances.

How does the randomization method impact previous Social Security numbers?

The randomization method impacted the SSN assignment process in the following ways:

  • The method eliminated the geographical significance of the first three digits of the SSN.
  • Randomization eliminated the significance of the highest group number.
  • Previously unassigned area numbers were introduced for assignment excluding area numbers 000, 666, and 900–999.

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