How the VIN check digit is calculated

Position 9 of every 17-character VIN is a check digit. It lets anyone confirm, with simple arithmetic, that a VIN was copied correctly. The method is defined in 49 CFR 565.15.

Step 1 — give every character a value

Digits keep their own value. Letters are assigned values from the regulation's table (I, O and Q have none because they are never used):

Step 2 — multiply by the position weight

Each of the 17 positions has a weight. Position 9 has weight 0, so the check digit itself does not affect the calculation:

Step 3 — add, divide by 11, read the remainder

Add the 17 products and divide the sum by 11. The remainder (0 to 10) is the check digit; a remainder of 10 is written as X.

Worked example: 1M8GDM9AXKP042788

351 ÷ 11 leaves a remainder of 10, so the check digit is X — the same character that sits in position 9 of the example.

What a mismatch means

If the calculated value differs from position 9, at least one character was copied or typed wrongly — by far the most common cause. The check catches most single-character mistakes but not all of them: letters that share a value, such as A and J, can be swapped without changing the result. The check digit is a U.S. requirement under 49 CFR 565; VINs of vehicles built for some other markets may not follow it, so a mismatch on an imported vehicle is not by itself proof of tampering. On a vehicle built for the U.S. market it should match. If a VIN on a title or listing fails the check, compare it with the VIN on the vehicle itself.

The VIN decoder runs this calculation instantly and shows the weighted sum and remainder.