Hungary’s IBAN is 28 characters with a fully numeric BBAN, pattern ^[0-9]{24}$. Underneath sits the pénzforgalmi jelzőszám, the domestic GIRO account number, one of the more intricately self-checking formats in the SEPA area.
Structure
The official registry example is HU42 1177 3016 1111 1018 0000 0000, a SWIFT registry test value, not a real account:
HU42- country code and IBAN check digits117- 3-digit bank code in the GIRO clearing system7301- 4-digit branch code6- first domestic check digit, covering the 7 digits of the bank and branch prefix111110180000000- the 15-digit account number0- second domestic check digit, covering the account number
The 9-7-3-1 weighting
Both domestic check digits use the same method: multiply the digits by the repeating weights 9, 7, 3, 1, sum the products, and the check digit is what brings the total to a multiple of 10. Because the two checks cover disjoint parts of the number, a Hungarian IBAN carries three independent integrity tests once the ISO MOD-97 wrapper is included. Validators implementing the Hungarian rules can detect fabricated numbers that generic IBAN checkers accept.
16-digit and 24-digit domestic forms
Domestically, many Hungarian accounts are still printed as 16 digits (two groups of 8), the short GIRO form used by some banks; others use the full 24 digits (three groups of 8). For IBAN purposes the 16-digit form is extended to 24 by appending eight zeros, which is why so many HU IBANs end in a long run of zeros, as the registry example does.
Hungary is an EU and SEPA member while keeping the forint, so the same IBAN serves domestic HUF transfers over GIRO’s instant payment system and euro SEPA payments. A structurally valid HU IBAN, even with both domestic checks passing, does not prove the account exists or identify its holder. That assurance comes from Verification of Payee name matching, not from any checksum.