What is the format of a Dutch postcode?

A Netherlands postcode is four digits followed by two letters, written with a space, for example 1011 AB. The first digit is never 0, and codes run from 1011 in Amsterdam up to 9999.

Which letter combinations are not allowed?

The combinations SA, SD and SS are deliberately not issued because of their historical associations. A code that is otherwise well-formed but ends in one of these is invalid.

Does the space matter?

Officially a single space separates the digits from the letters (1011 AB). This validator accepts the code with or without the space and returns the canonical spaced form.

Does a valid format mean the address exists?

No. Format validation confirms the code could be a real Dutch postcode, not that it maps to a delivered address. Combine it with a house number and a postcode database (PostNL) for full verification.

Is my data sent anywhere?

No. The check runs entirely in your browser; the postcode never leaves your device.

Netherlands Postal Code Validator

A Dutch postcode uniquely pins down a street or part of a street and, with a house number, identifies an exact delivery point. The format is strict — four digits and two letters — which makes it easy to validate before you accept an address at checkout. This free tool runs that check in your browser.

How it works

The validation rules are:

Digits. Exactly four digits, and the first digit is never 0 (codes start at 1011).
Letters. Exactly two uppercase letters after the digits.
Reserved combinations. The letter pairs SA, SD and SS are not issued and are rejected.
Spacing. The canonical form puts a single space between the digits and letters (NNNN AA), which the tool reconstructs for you.

Example

1011 AB passes: four digits with a non-zero leading digit, two letters, and AB is not a reserved pair. 0123 AB fails on the leading zero, and 1234 SS fails on the reserved letter pair.

Notes

A valid format does not guarantee the postcode is in active use or matches a specific house number. For deliverable-address certainty, check against the official PostNL postcode database. Everything here stays on your device.