The 9th character of a VIN encodes a mod-11 check digit that validates the whole VIN. It falls in the Check digit block of the 17-character VIN. Below is exactly what it means, with a real sample VIN highlighting the 9th position.
Here the check digit is 4 — the mod-11 checksum of the other 16 characters.
The 9th character is the check digit — a single value (0–9 or X) computed from the other 16 characters using a weighted mod-11 formula. It exists purely to catch typos: change any one character and the check digit almost always stops matching.
Each character is transliterated to a number, multiplied by its position weight, summed, and reduced mod 11; a remainder of 10 is written as X. See the full worked calculation.
Decode a full VIN → · See all 17 positions →
← 8th character · 10th character →
It encodes a mod-11 check digit that validates the whole VIN. In the sample JA4APUAU4J8605306 the 9th character is 4.
The check digit — a mod-11 checksum over the other 16 characters that verifies the VIN was typed correctly.
X represents the value 10, used whenever the mod-11 remainder is exactly 10. It is a valid check digit, not a letter.
Transliterate each character to a number, multiply by the position weight (8,7,6,5,4,3,2,10,0,9,8,7,6,5,4,3,2), sum, and take mod 11.