Why does the DOL ask about twins?

The Washington State Department of Licensing (DOL) is unique in that it encodes your last name, first and middle initial, and your date of birth in your driver’s license or identification card number. Based on this formula, twins have the potential to generate the same license number. These license numbers look like the following:


  • LLLLL – Last Name, truncated – The first five characters are the first five letters of the last name. If the name is shorter than five characters, the extra space is padded with asterisks (*).
  • F – First Initial
  • M – Middle Initial
  • YY – Year of birth, encoded – This is 100 minus the two digit year of birth. So someone born in 1915 will be 85 (100-15), as would someone born in 2015.
  • X – Checksum – calculated from the rest of the license
  • Month of Birth, encoded:
  • Day of birth, encoded:twinday

Based on this formula, the following is an example of a twin pair that could have the same license number:

  • WOO**JT547KA
    • “John T. Woo,” born on May 1st, 1946
  • WOO**JT5462A
    • “Joe T. Woo,” born on May 1st, 1946

To avoid issuing a duplicate driver’s license number, the DOL asked both John & Joe if they are a twin. John was the first twin to request a license from the DOL, so his month of birth is encoded with the character from column 1, above. Joe was the second twin, so his month of birth is encoded with the character from column 2. The DOL compiles a list of these names on a weekly basis and forwards them to the Twin Registry. Invitations are sent out on a monthly basis.

Occasionally twinship is indicated accidentally by the DOL. In these instances an individual may receive an invitational packet when they are not actually a twin. Unfortunately, we have no way of knowing ahead of time if someone is in fact a twin. If you received an invitational packet and you are not a twin, please send us an email and let us know.