How is the Irish VAT check letter calculated?

Multiply the seven numeric positions by weights 8,7,6,5,4,3,2, sum them, and take modulo 23. Map the remainder to a letter where 0 is W and 1 to 22 are A to V. The new two-letter format adds the second trailing letter at weight 9.

What are the four Irish VAT formats?

The formats are seven digits plus one check letter; the old layout with a letter, plus, or asterisk in the second position; and the post-2013 format of seven digits plus two letters. Each shares the same mod-23 check on the numeric body.

Why does my Irish VAT have a letter in the middle?

Businesses registered before 2013 sometimes carry a letter, plus sign, or asterisk in the second position. For the checksum that second character is treated as a zero, so the body is the leading digit followed by a zero and the remaining five digits.

Does a valid check letter mean the business is VAT-registered?

No. A valid check letter only confirms the number is internally consistent. To confirm current registration, use the EU VIES service or Irish Revenue. This tool performs no online lookup.

Is my VAT number sent anywhere?

No. The whole validation runs in your browser. The VAT number never leaves your device, so it is safe for confidential supplier records.

Ireland VAT Number Validator

An Irish VAT number is the registration identifier issued by Irish Revenue to VAT-registered businesses. Over the years Ireland has used several layouts, so a robust validator must recognise all four and apply the same mod-23 check letter rule. This free tool does exactly that, in your browser.

How it works

Every Irish VAT number carries a single check letter computed from the seven-character numeric body:

Strip the IE prefix and spaces, then detect the format:
- Format 1: seven digits plus one check letter, e.g. 6388047V.
- Format 2 (legacy): one digit, then a letter, +, or *, then five digits, then the check letter, e.g. 1A23456T. The second character counts as zero in the sum.
- Format 3 (post-2013): seven digits plus two trailing letters, e.g. 1234567FA.
Multiply the seven body characters by the weights 8, 7, 6, 5, 4, 3, 2 and sum the products.
For the two-letter format, add the value of the second trailing letter (A is 1) multiplied by 9.
Take the sum modulo 23. Map the remainder to a letter: 0 becomes W, and 1 through 22 become A through V.
The number is valid when that computed letter equals the supplied check letter.

Example

Validate 6388047V. The body 6388047 against weights 8,7,6,5,4,3,2 gives 48 + 21 + 48 + 40 + 0 + 12 + 14 = 183. Then 183 mod 23 = 22, and 22 maps to the letter V. That matches the supplied check letter, so 6388047V is valid.

Notes

A valid check letter confirms the number is well-formed, not that the business is currently VAT-registered — check VIES or Irish Revenue for that. Everything here runs locally, so your VAT number never leaves your device.