VIN check digit

What the check digit is

Position 9 of a VIN carries no information about the vehicle. It is a check digit: a single character calculated from the other sixteen, defined by ISO 3780 and required on every vehicle sold in North America since 1981. Its job is to catch a transcription error — an 8 read as a B, a 5 as an S, two characters swapped — before that error becomes a wrong record.

The arithmetic, in three steps

1. Transliterate. Each digit is worth itself. Each letter is worth the value in the first table below. I, O and Q have no value because they never appear in a VIN at all — they are excluded so they cannot be confused with 1 and 0.
2. Weight and sum. Multiply each of the seventeen values by the weight for its position, from the second table, and add the products. Position 9 has a weight of zero, which is how the check digit avoids checking itself.
3. Take the remainder. Divide the sum by 11. The remainder is the check digit — except that a remainder of ten is written X, because it needs a single character and the digits are used up.

What a disagreement proves, and what it does not

It does not prove the VIN is fake. The check digit is mandatory in North America and optional almost everywhere else, so a car built in Europe or Japan for a non-US market may carry a ninth character that means nothing at all. A great many legitimate imports fail this test. That is why the decoder on this site decodes a VIN whose check digit disagrees rather than refusing it, and flags the disagreement alongside the answer.

What a disagreement does prove is that the seventeen characters in front of you are not internally consistent. If the vehicle was built for the North American market, the overwhelmingly likely explanation is that one character was misread or mistyped — and the second most likely is that the VIN was invented by somebody who did not know about this arithmetic.

And an agreement proves very little. Any competent forger can calculate a check digit; this page just did it. A valid check digit means the number is well-formed, not that the vehicle exists, that the plate matches it, or that its history is clean. Nothing on this site can tell you those things, and we say plainly which of them we refuse to pretend to.