Ireland VAT Number Validator (Irish VAT Registration)
Validate Irish VAT numbers in standard 8-character and modern 9-character formats via Modulo 23.
About the Irish VAT Number
The Irish VAT Number is issued by the Revenue Commissioners to businesses registered for value-added tax in Ireland.
As Ireland hosts European headquarters for major global tech companies, this identifier is essential for cross-border software billing.
Anatomy & Structure of Irish VAT
The Irish VAT number consists of the 'IE' prefix followed by 8 or 9 alphanumeric characters:
| Position | Field | Length | Meaning & Rule | Example |
|---|---|---|---|---|
| 1 to 2 | Country Code | 2 characters | Fixed prefix 'IE' (ISO 3166-1 alpha-2) | IE |
| 3 to 9 | Base Number | 7 digits | Sequential registration number issued by Revenue | 1234567 |
| 10 | Check Character | 1 letter | Alphabetical check character calculated via Modulo 23 | T |
| 11 | Optional Suffix | 1 letter | Second letter in modern post-2013 expanded format | A |
Official Revenue Commissioners Algorithm (Modulo 23)
Weighted calculation rule under Irish tax legislation:
Sum = Σ(d[i] * W[i]) [W = 8, 7, 6, 5, 4, 3, 2] + (L2 - 64) * 9; Char = Rem === 0 ? 'W' : Char(64 + Rem)
- 1. Extract the first 7 numeric digits of the VAT number.
- 2. Multiply each digit by weights [8, 7, 6, 5, 4, 3, 2] and sum up the products.
- 3. If a second letter is present (9-char format), add (ord(L2) - 64) * 9 to the sum.
- 4. Calculate the remainder modulo 23.
- 5. If remainder is 0, the expected character is 'W'; otherwise, map remainder to letters (1='A' to 22='V').
- 6. Confirm that the 8th position matches the calculated check letter.