How the VIN Check Digit Is Calculated

Where the check digit is

In VINs used in North America, position 9 is a check digit computed from the other 16 characters. It is a number 0–9 or the letter X (representing 10).

Extracting It Automatically

When you read this data from photos, the VIN OCR API returns it as structured JSON, and you can apply the rules on this page as validation. Try it with the free scanner.

Where This Fits

• Step 1: transliterate letters: Letters are converted to numbers: A=1, B=2, C=3, D=4, E=5, F=6, G=7, H=8, J=1, K=2, L=3, M=4, N=5, P=7, R=9, S=2, T=3, U=4, V=5, W=6, X=7, Y=8, Z=9. Digits keep their value.
• Step 2: apply weights: Multiply each value by its position weight: 8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2 for positions 1–17. Position 9 has weight 0.
• Step 3: take the remainder: Add the products and divide by 11. The remainder is the check digit; a remainder of 10 is written as X.

Python Implementation

A minimal, dependency-free implementation you can use to validate OCR output.

Prerequisite: Python 3.9+

MAP = {**{str(d): d for d in range(10)}, **dict(zip("ABCDEFGH", range(1, 9))), **dict(zip("JKLMN", range(1, 6))), "P": 7, "R": 9, **dict(zip("STUVWXYZ", range(2, 10)))}
WEIGHTS = [8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2]

def vin_check_digit_ok(vin: str) -> bool:
    vin = vin.upper()
    if len(vin) != 17 or any(c not in MAP for c in vin):
        return False
    remainder = sum(MAP[c] * w for c, w in zip(vin, WEIGHTS)) % 11
    return vin[8] == ("X" if remainder == 10 else str(remainder))

print(vin_check_digit_ok("1M8GDM9AXKP042788"))

Reference Summary

Key facts from this page in structured form, for quick lookup.

{
  "Where the check digit is": "In VINs used in North America, position 9 is a check digit computed from the other 16 characters.",
  "Step 1: transliterate letters": "Letters are converted to numbers: A=1, B=2, C=3, D=4, E=5, F=6, G=7, H=8, J=1, K=2, L=3, M=4, N=5, P=7, R=9, S=2, T=3, U=4, V=5, W=6, X=7, Y=8, Z=9.",
  "Step 2: apply weights": "Multiply each value by its position weight: 8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2 for positions 1–17.",
  "Step 3: take the remainder": "Add the products and divide by 11."
}