BSN Validator (Netherlands)

How it is calculated

The tool removes everything that is not a digit (spaces, dots, dashes and even letters), so "111 222 333" works. An 8-digit number gets a leading zero to make 9 digits. Anything with fewer than 8 or more than 9 digits is marked not valid straight away. Then the nine digits d₁…d₉ are weighted: sum = 9·d₁ + 8·d₂ + 7·d₃ + 6·d₄ + 5·d₅ + 4·d₆ + 3·d₇ + 2·d₈ − 1·d₉. The number passes the eleven-test when sum mod 11 = 0. The remainder is shown so you can see how far off a failing number is.

The all-zero number 000000000 is also rejected, although its sum is 0. This only checks the internal checksum of the digits. It cannot tell whether the number was ever issued to a person, and it does not check the owner's name or birth date.

Common mistakes

• Treating "valid" as "real". A number that passes the eleven-test only has a consistent checksum; many passing numbers have never been issued to anyone.
• Adding extra digits by accident, for example a country code or a second copy of a digit. Anything beyond 9 digits is rejected, while letters such as NL are simply dropped.
• Typing 8 digits and expecting an error. Some older numbers are written with 8 digits, and the tool adds the leading zero itself.
• Using the same check for the Dutch A-number, a phone number or an IBAN. Those have different rules; this test is specific to the BSN.
• Reading a small remainder as "almost correct". A remainder of 1 or 10 does not mean one digit is off by one; the checksum only says whether the sum is divisible by 11.