Sao Tome and Principe IBAN validator

A São Tomé and Príncipe IBAN is 25 characters, entirely numeric: “ST”, two check digits, a 4-digit bank code, a 4-digit branch code, an 11-digit account number, and 2 national check digits folded into the very end of the string, on top of the two IBAN-level check digits at the front. That 25-character, all-numeric layout isn’t a coincidence — it matches Portugal’s own IBAN in both length and digit count, a legacy of São Tomé and Príncipe’s history as a former Portuguese colony whose banking numbering system followed Portugal’s model even after independence. Unlike Portugal’s IBAN, though, which folds everything into one continuous 21-digit block, São Tomé and Príncipe’s format explicitly separates bank code, branch code, account number, and a dedicated pair of national check digits — four segments doing the same job Portugal’s single block does.

How this validator works

This tool checks the “ST” prefix and confirms all 23 remaining characters are digits, split into a 4-digit bank code, 4-digit branch code, 11-digit account number, and 2 national check digits, then runs the mod-97 checksum (ISO 7064) — entirely in your browser, nothing sent to a server.

What a pass doesn’t tell you

A pass confirms the 25 digits are correctly structured and internally consistent — not that the account is open or belongs to whoever you expect. This tool does no lookup against the Central Bank of São Tomé and Príncipe or any commercial bank there. If a São Tomé and Príncipe IBAN fails, check the trailing 2 national check digits first — a segment with no letters to anchor your eye on is where a transposed digit is easiest to miss.

Scope: São Tomé and Príncipe IBAN structure and mod-97 checksum validation only — not payment processing or confirmation an account is active. Use it to catch a typo before a transfer fails.

Content last reviewed 2026-07-23.