How does the UK VAT check digit work?

The first 7 digits are multiplied by weights 8,7,6,5,4,3,2 and summed. The 2-digit check value is added. The number is valid if the total is divisible by 97 (old style) or if the total plus 55 is divisible by 97 (new style). This tool accepts either, like HMRC's own validator.

What is the difference between old-style and new-style UK VAT numbers?

The original "9755" check (old style) requires the weighted sum plus the check value to be divisible by 97. When that number space ran out, HMRC introduced a new-style variant that adds 55 before the mod-97 test. Numbers issued under either scheme are valid, so this tool passes a number that satisfies either.

How many digits is a UK VAT number?

A standard UK VAT number is 9 digits, often shown with a GB prefix, e.g. GB 123 4567 89. Some have 12 digits, where the extra 3 digits are a branch suffix. This tool validates the check digit on the first 9 digits in both cases.

Does a pass mean the business is VAT-registered?

No. A passing check digit means the number is internally consistent, not that it is registered or active. Confirm registration on the official HMRC service. This tool performs no lookup.

Does this tool handle the GB prefix and spaces?

Yes. It strips an optional GB prefix and any spaces, dots or dashes before checking, so GB 123 4567 89 and 123456789 are treated identically. Government (GD) and health-authority (HA) style numbers are out of scope.

Is my VAT number sent anywhere?

No. The check digit is computed entirely in your browser — privacy-first, the number never leaves your device.

UK VAT Number Validator

UK VAT number validator

Every UK VAT number ends in a self-checking digit, so a single mistyped figure usually makes the whole number fail. This tool verifies that check digit using HMRC’s own weighted mod-97 algorithm — no online lookup — which is exactly what you want for invoice validation, supplier onboarding, or catching a typo before you submit a return.

How it works

The tool strips an optional GB prefix and any spaces, then validates the first 9 digits:

Multiply the first 7 digits by the weights 8, 7, 6, 5, 4, 3, 2 and sum them.
Add the 2-digit check value (digits 8–9) to that weighted sum.
Old style: the total must be divisible by 97.
New style: the total plus 55 must be divisible by 97.

A number passes if it satisfies either scheme — matching HMRC’s behaviour. A 12-digit number is handled as 9 core digits plus a 3-digit branch suffix, with the check applied to the first 9.

Example

Validate GB 123 4567 89 (base 1234567, check 89):

Digit	1	2	3	4	5	6	7
Weight	8	7	6	5	4	3	2
Product	8	14	18	20	20	18	14

Weighted base sum = 112. Old style: (112 + 89) = 201, not divisible by 97 → fail. New style: (112 + 89 + 55) = 256, also not divisible by 97. A genuine VAT number whose check value is chosen correctly will make one of those totals land exactly on a multiple of 97 and show Valid check digit.

Privacy: the calculation runs locally with no HMRC lookup, so a pass confirms the number is well-formed — not that the business is registered. Verify registration on the official HMRC service.