The 9th character of a VIN is not a random assignment.

It’s a calculated value derived from the other 16 characters using a formula NHTSA standardized under 49 CFR Part 565. Run the math wrong and you get a different result, which means a VIN that fails the check didn’t come from the factory.

This matters when you’re looking at a used car and want to know whether the VIN has been altered.

For the full position-by-position breakdown of the VIN, see how to read a VIN number.

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The formula

Each character in a VIN is assigned a numeric value. Letters get mapped to numbers; digits keep their face value. Then each value is multiplied by a positional weight. The products are summed, and the sum is divided by 11.

The remainder is the check digit, except when the remainder is 10, in which case the check digit is “X.”

Transliteration table (letters to numbers):

Letter	Value	Letter	Value
A	1	N	5
B	2	P	7
C	3	R	9
D	4	S	2
E	5	T	3
F	6	U	4
G	7	V	5
H	8	W	6
J	1	X	7
K	2	Y	8
L	3	Z	9
M	4

Digits stay as-is. Letters I, O, and Q don’t appear in VINs at all, they’re excluded to avoid visual confusion with 1, 0, and 0.

Positional weights:

Position	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17
Weight	8	7	6	5	4	3	2	10	0	9	8	7	6	5	4	3	2

Position 9 gets weight 0 because that’s the check digit itself, excluding it from its own calculation.

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A worked example

VIN: 1HGCM82633A004352

Pos	Char	Value	Weight	Product
1	1	1	8	8
2	H	8	7	56
3	G	7	6	42
4	C	3	5	15
5	M	4	4	16
6	8	8	3	24
7	2	2	2	4
8	6	6	10	60
9	3	—	0	0
10	3	3	9	27
11	A	1	8	8
12	0	0	7	0
13	0	0	6	0
14	4	4	5	20
15	3	3	4	12
16	5	5	3	15
17	2	2	2	4

Sum: 311 ÷ 11 = 28 remainder 3

The check digit is 3, which matches position 9. This VIN is valid.

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What a failed check digit actually means

A VIN that fails the check digit test was either:

• Mistyped (most common)
• From a pre-1981 vehicle (the formula wasn’t standardized until 1981, see classic car VIN decoding)
• From a non-US vehicle that doesn’t follow the NHTSA standard (some Canadian, European, and Asian manufacturers use different schemes for domestic-market vehicles)
• Deliberately altered

The last one is the concerning scenario. VIN tampering, changing characters to obscure a salvage title, a theft record, or a rollback, is a federal crime. But it happens. If a VIN fails the check digit and the car was supposedly built after 1981 for the US market, that’s a red flag worth following up on before you sign anything.

A check digit failure alone doesn’t confirm fraud. It’s a signal to look harder. Pull a full vehicle history report and compare the dashboard VIN against the door jamb, the firewall stamp, and the title. If any of those don’t match, walk away.

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FAQs

What is the check digit in a VIN?
It’s the 9th character, calculated from the other 16 using a weighted formula. It lets you verify that a VIN wasn’t mistyped or altered.

What if my VIN has an X in position 9?
X is valid. It represents a check value of 10, which can’t be expressed as a single digit, so NHTSA designated X as the placeholder.

Does every VIN have a valid check digit?
No. Pre-1981 vehicles weren’t subject to the standardized formula. Non-US-market vehicles may also use different formats. Use VinDecoderPlus to verify, the decoder flags check digit status automatically.