Vehicle Checksum Formula

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The checksum, also known as the last alphabet of a vehicle license plate, of a bus registration number is derived from the following formula.

Prefix
SG 11 – (5 × 1st No.) – (4 × 2nd No.) – (3 × 3rd No.) – (2 × 4th No.)
SBS 2 – (5 × 1st No.) – (4 × 2nd No.) – (3 × 3rd No.) – (2 × 4th No.)
SMB 9 – (5 × 1st No.) – (4 × 2nd No.) – (3 × 3rd No.) – (2 × 4th No.)
TIB 7 – (5 × 1st No.) – (4 × 2nd No.) – (3 × 3rd No.) – (2 × 4th No.)

Suffix Table

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0
A B C D E G H J K L M P R S T U X Y Z
  • Note: Letters F, I, N, O, Q, V & W are omitted.

Example

For example, the registration plate of SG5999.

Using the above formula for SG-prefixed plates, you should get a statement like this: 11–(5×5)–(4×9)–(3×9)–(2×9). A quick input of the statement on Google should give a result of -95.

Using the result, mod the number with 19, you will get a number from 0 to 18. You can mod the number by 19 using Google. For the above example where the result is -95, type -95 mod 19 into the Google search bar and it would calculate the answer, 0.

Compare the answer against the table above for the suffix.

Hence the checksum for SG5999 is Z.

How "Mod 19" works

Mod 19 works in a way that the number 19 is deducted from a number until the remainder reaches 18 or less.

For example, if you get a result of -95 from the given formula.

  1. Remove the minus sign (modulus)
  2. Deduct 19 from 95 as many times as you can before remainder reaches 18 or less
    95 - 19 - 19 - 19 - 19 - 19 = 0
  3. Substitute remainder 0 with the letter Z and it will be the suffix of the license plate