A Y-tunnus is the Finnish business ID assigned by the Finnish Patent and Registration Office (PRH) and the Tax Administration (Vero) to every registered business. It appears on invoices, contracts, and registry records, so confirming one is well-formed before relying on it avoids data-entry mistakes. This validator runs the official modulus-11 check in your browser.
How it works
A Y-tunnus is 7 body digits plus 1 check digit. The check digit is verified with a weighted modulus-11 algorithm:
- Multiply the 7 body digits by the positional weights 7, 9, 10, 5, 8, 4, 2.
- Add the products to get a weighted sum.
- Compute
remainder = sum mod 11. - If the remainder is 0, the check digit is 0. If the remainder is 1, no valid check digit exists and the number is invalid. Otherwise the check digit is
11 − remainder. - The Y-tunnus is valid when the expected check digit matches the given one.
Example
For 0737546-2, the weighted sum of the seven body digits produces a remainder under modulus 11 that yields an expected check digit of 2, which matches the digit after the hyphen, so the number passes.
Notes
A passing checksum confirms the format is correct, not that the business exists. To verify registration, look the Y-tunnus up in the PRH or Vero registry. The whole check runs locally, so the Y-tunnus you enter never leaves your browser.