OIB (Personal Identification Number) is the Croatian unique 11-digit identifier for all natural and legal persons. Introduced in 2008 to replace MBG (citizen number), MBR (worker number), and various tax numbers with one code. This guide explains the algorithm, validation, and how to use it.
OIB is an 11-digit number assigned by the Croatian Ministry of Finance. Assigned to: all Croatian citizens at birth (or residence registration), all legal entities upon founding, foreign persons with resident status, foreign legal entities operating in Croatia. Not the same as JMBG, MBG, MBR — those are old systems. OIB is not random: first 10 digits are a serial number, 11th is the check digit computed by modulo 11 algorithm.
Algorithm: take first 10 digits, multiply each by weights 10, 9, 8, 7, 6, 5, 4, 3, 2 (right to left), sum. Divide sum by 11, subtract remainder from 10. If result = 10, check digit = 0. Otherwise = result. Example: OIB 1234567890X — weighted sum = 138, 138 mod 11 = 6, 10 - 6 = 4. If 11th digit is 4 → valid. Otherwise → invalid.
FINA Court Registry is the public database of all Croatian legal entities. API endpoint returns: name, OIB, headquarters (street, number, city), MB (registry number), founding date, status (active/bankruptcy/liquidation), activity (NKD), capital. Lookup free up to 100 searches per month, paid per search above. All retrieved data can be used in CRM, invoicing, AML processes.
Croatian Anti-Money Laundering Act (NN 108/17) obliges entities (banks, fintech, accountants, lawyers, brokers, gambling) to perform KYC for all clients. KYC contains: OIB validation, Court Registry check, screening against PEP (Politically Exposed Persons) and EU/UN sanctions lists. Re-screening every 24 hours for high risk, annually for low. Documentation storage 5 years after relationship termination.
Talk to us about how the 4b2b ecosystem fits into your existing Fiscalization 2.0 flow. We have implementations from 50-employee firms to ZSE-listed companies.
