How does the VIN check digit work?

Each of the 17 characters is converted to a number, multiplied by a fixed positional weight, and the products are summed. The sum is divided by 11 and the remainder becomes the check digit, where a remainder of 10 is written as the letter X. That value must match position 9.

Why are I, O, and Q not allowed in a VIN?

Those letters are excluded everywhere in a VIN because they are easily confused with the digits 1 and 0. If they appear, the VIN is malformed. The tool flags them rather than silently substituting digits.

Does a valid check digit mean the VIN is real?

No. A passing check digit only proves the 17 characters are internally consistent and free of common typos. It does not confirm the vehicle exists or its history. Use a title or NHTSA lookup for that.

Is the check digit required outside North America?

The check digit at position 9 is mandatory for vehicles sold in North America under FMVSS and Transport Canada rules. Many vehicles built for other markets do not compute a check digit, so a non-North-American VIN may legitimately fail this test.

What does a check digit of X mean?

When the weighted sum divided by 11 leaves a remainder of 10, that single character cannot be a digit, so the standard writes it as the letter X. An X in position 9 is valid and expected for those VINs.

VIN Check Digit Validator

The ninth character of a North American VIN is a check digit, mathematically derived from the other 16. This validator runs the exact NHTSA algorithm to confirm it matches, catching transposed or mistyped characters that would otherwise slip through. Everything happens in your browser.

How it works

Each character maps to a value, gets multiplied by a positional weight, and the weighted sum is reduced modulo 11:

value(char)   per NHTSA transliteration table (A=1 … with I,O,Q excluded)
weights       8 7 6 5 4 3 2 10 0 9 8 7 6 5 4 3 2   (position 9 weight is 0)
sum           Σ value(charᵢ) × weightᵢ
check digit   sum mod 11, where 10 → "X"
valid         computed check digit == character at position 9

The weight at position 9 is zero, so the check digit never feeds its own calculation. A remainder of 10 is written as X.

Example and tips

Take a VIN ending in a known-good check digit, swap any two adjacent characters, and the validator flips to invalid — that is exactly the class of error it is built to catch. Remember a legitimate non-North-American VIN may fail because it was never assigned a computed check digit, and that an X in position 9 is a normal, valid outcome, not an error.