Netherlands postcode validator
How the postcode format works
- Format
- 4 digits followed by 2 letters
- Example
- 1011AB
Things to watch for
- Format-only check — does not confirm the postcode actually exists
- 4 digits + 2 letters; normally written with a space between them (e.g. 1011 AB)
^[0-9]{4}[A-Z]{2}$A Dutch postcode is the address code PostNL uses to route mail, combining 4 digits with 2 letters — for example 1011 AB in central Amsterdam. Because that combination narrows mail down to street level (sometimes to a handful of addresses), a single wrong character can point to a completely different street than intended. Anyone validating a shipping address, a checkout form, or a spreadsheet of Dutch customer records needs the postcode correctly shaped before it’s trusted.
The digit-then-letter structure also makes a common mistake easy to catch: entering the letters first, using lowercase where the system expects uppercase, or dropping a digit so the string is one character short. All of these produce something that clearly isn’t a valid Dutch postcode shape, even before checking whether the specific combination is real.
How this validator works
This tool checks that the input is exactly 4 digits followed by 2 letters, accepting the postcode with or without the customary space between them, entirely in your browser with nothing sent to a server.
What a pass doesn’t tell you
A Dutch postcode carries no check digit, so matching the 4-digit-plus-2-letter shape is the most a client-side tool can confirm — not that PostNL has assigned that specific combination to a real street. Confirming that, and seeing the exact address range it covers, requires PostNL’s own postcode lookup.
Scope: format validation only — not address lookup, street-level matching, or confirming a postcode is currently in use.
postcode FAQ
Why is a Dutch postcode so precise compared to other countries?
PostNL's 4-digit + 2-letter combination (e.g. 1011 AB) is deliberately fine-grained: the 4 digits narrow mail down to a small area of a town, and the 2 letters typically pin it to one street or a short stretch of one — often just a few dozen addresses. That's far more granular than a plain 4- or 5-digit postcode used elsewhere.
Do I need to type the space between the digits and letters?
No — this validator accepts the postcode with or without the space (e.g. '1011AB' or '1011 AB'). The space is a formatting convention; the underlying code is still 4 digits followed by 2 letters.
Does a correctly formatted postcode mean it actually exists?
No. This tool only confirms the string is 4 digits followed by 2 letters — it doesn't check the combination against PostNL's actual address list. Confirming a Dutch postcode is real, and seeing which street it maps to, requires PostNL's own postcode lookup.