What is the BSN elfproef and how does it work?

The elfproef (eleven-test) is a weighted checksum. The 9 digits d1–d9 are multiplied by weights 9, 8, 7, 6, 5, 4, 3, 2 and −1 respectively. Their sum S must satisfy two conditions: S mod 11 = 0 and S is not zero. The −1 weight on the last digit is what makes the test distinctive — it subtracts the final digit rather than adding it.

Why does an 8-digit BSN get a leading zero?

Older Dutch BSNs were issued as 8-digit numbers. The elfproef formula is defined over exactly 9 digit positions, so any 8-digit BSN is left-padded with one zero before the calculation. The padded form is shown in the "Normalised" row of the results table.

What information is encoded inside a BSN?

None. Unlike Finland's HETU, Romania's CNP or China's resident ID, the Dutch BSN is an opaque sequential number. It does not encode birth date, gender, region or any other personal attribute. The only structural property is that it must satisfy the elfproef.

What does a failed 11-test mean in practice?

The number is not a structurally valid BSN. Common causes are a transcription error (one digit wrong), a transposition (two adjacent digits swapped) or a fabricated number. Single-digit errors almost always change the weighted sum by a non-multiple of 11, so the test catches them reliably. Check the number against the original document.

Does passing the 11-test prove the BSN is issued to a real person?

No. The elfproef is a mathematical filter — it rejects malformed numbers but cannot confirm the number exists in the Basisregistratie Personen (BRP) or belongs to any individual. Only the Dutch government holds that information.

Is it legal to use this tool to generate or guess BSNs?

This tool only validates numbers you already have — it does not generate BSNs. Deliberately constructing or using a valid-looking BSN to impersonate someone is identity fraud under Dutch law (Wetboek van Strafrecht art. 231). Use this tool only for legitimate verification of your own number or numbers for which you have lawful authorisation.

Netherlands BSN Validator

The Burgerservicenummer (BSN) is the Netherlands’ national citizen-service number. Every Dutch resident receives one at birth or on first registration with a municipality. It appears on passports, identity cards, tax returns, healthcare registrations and a wide range of government services. This validator checks whether a given 8- or 9-digit number is structurally correct by running the official elfproef (eleven-test) — the same weighted checksum that Dutch government systems apply — entirely inside your browser.

What the BSN looks like

A BSN is a sequence of 8 or 9 decimal digits with no letters, hyphens or other separators embedded in the number itself. In official documents it is sometimes written as three groups of three digits (e.g. 123 456 789), but that spacing is cosmetic only. Older numbers issued before 2007 were 8 digits long; newer numbers are 9. The validator accepts both forms and zero-pads 8-digit inputs on the left before running the checksum.

The elfproef — how the 11-test works

The checksum formula multiplies each of the nine digits by a fixed weight and sums the results:

S = 9·d1 + 8·d2 + 7·d3 + 6·d4 + 5·d5 + 4·d6 + 3·d7 + 2·d8 + (−1)·d9

Two conditions must both hold for the BSN to be valid:

S mod 11 = 0 — the weighted sum must be divisible by eleven.
S ≠ 0 — the all-zeros string 000000000 is reserved and not issued.

The critical design detail is the negative weight on the final digit. This is not a typo in the standard: it means the last digit is subtracted rather than added to the running total. As a result, swapping any single digit changes S by a non-multiple of 11 in almost every case, giving the test strong single-digit error-detection.

Worked example

Take the obviously-fake test number 111 222 333:

d1	d2	d3	d4	d5	d6	d7	d8	d9
1	1	1	2	2	2	3	3	3
×9	×8	×7	×6	×5	×4	×3	×2	×(−1)
9	8	7	12	10	8	9	6	−3

Sum S = 9 + 8 + 7 + 12 + 10 + 8 + 9 + 6 − 3 = 66. 66 ÷ 11 = 6 exactly, so 66 mod 11 = 0 and S ≠ 0 — the number passes.

The tool’s “Show full weighted calculation” panel reproduces this table live for any number you enter, with the final-digit weight highlighted in red so the subtraction step is always visible.

What the BSN does NOT encode

Unlike some national identifiers — Finland’s HETU encodes birth date and gender, Romania’s CNP encodes birth year, gender and county — the Dutch BSN is an opaque sequential number. No personal attributes are encoded in the digits. The validator therefore reports only whether the checksum passes; there is no birth-date, gender or region information to decode.

Privacy

Every calculation runs locally in your browser using pure JavaScript. No BSN, no intermediate value and no result is ever transmitted to a server. The page makes no network requests during validation.