How long is a KvK number?

A modern KvK (Kamer van Koophandel) number is exactly 8 digits. Numbers issued from 2008 onward are standardised to this length and carry a check digit; older registrations may differ.

What is the elfproef?

The elfproef, or 11-test, is the Dutch check used by KvK and BSN numbers. Each digit is multiplied by a positional weight, the products are summed, and the number is valid if the sum is divisible by 11.

Which weights are used?

For the eight digits from left to right the weights are 8, 7, 6, 5, 4, 3, 2 and -1. The negative weight on the final digit is part of the standard Dutch 11-proef convention.

Does a valid check mean the company is active?

No. Passing the 11-proef only confirms the number is internally consistent. To confirm a company is currently registered and trading, look it up in the official KvK Handelsregister.

Is my KvK number sent anywhere?

No. The format and 11-proef checks run entirely in your browser, so the number never leaves your device.

Netherlands KvK Number Validator

A KvK number is the 8-digit identifier the Dutch Chamber of Commerce (Kamer van Koophandel) assigns to every registered business in the Netherlands. Procurement and finance teams use it to verify that a supplier is properly registered. This validator checks the format and applies the Dutch elfproef (11-test) so you can catch typos before relying on the number.

How it works

KvK numbers issued from 2008 onward are standardised to 8 digits with a check built into the 11-proef:

Strip non-digits and confirm there are exactly 8.
Multiply each digit by its positional weight: 8, 7, 6, 5, 4, 3, 2, -1 from left to right.
Sum the products.
The number passes if that sum is divisible by 11 (remainder 0).

The final digit carries a weight of -1, which is the standard convention shared with the Dutch BSN check.

Example

For 90004760, multiply the digits by the weights and sum: the weighted total is a multiple of 11, so the remainder is 0 and the number passes the 11-proef. By contrast 69599084 leaves a remainder of 3 and fails.

Notes

The 11-proef applies to numbers issued from 2008 onward. A pass confirms the number is internally consistent, not that the company is currently active or solvent. For real registration status, query the official KvK Handelsregister. Everything here runs locally in your browser.