How is a New Zealand IRD number validated?

The number is 8 or 9 digits with a check digit at the end. The base (without the check digit) is left-padded to 8 digits and must fall between 10,000,000 and 150,000,000. The 8 base digits are multiplied by primary weights 3,2,7,6,5,4,3,2 and summed; the check digit is 11 minus (sum mod 11), or 0 if that remainder is 0. If the result is 10, the calculation is repeated with secondary weights 7,4,3,2,5,2,7,6; if it is still 10 the number is invalid.

What is an IRD number?

An IRD number is the unique tax identifier issued by New Zealand's Inland Revenue to individuals and organisations. It is 8 or 9 digits and is used for income tax, GST, KiwiSaver and other tax dealings.

Why are there two sets of weights?

When the primary weights produce a check digit of 10, that single value cannot be represented in one digit, so Inland Revenue's algorithm recalculates with a secondary set of weights. If the secondary pass also yields 10, the number is invalid by design.

Does a valid check digit mean the IRD number is registered?

No. The check digit only confirms the number is mathematically well-formed and in the valid range. It cannot tell you whether the IRD number was actually issued or who holds it, and this tool never contacts Inland Revenue.

What range of base numbers is valid?

The base (the number without its trailing check digit) must fall between 10,000,000 and 150,000,000. Numbers outside that range are rejected before the check digit is even tested.

Is my IRD number sent anywhere?

No. The validator is privacy-first. The check digit calculation runs locally in your browser with JavaScript — there are no network requests and your IRD number never leaves your device.

New Zealand IRD Number Validator — Check Digit Verification

An IRD number is the tax identifier issued by New Zealand’s Inland Revenue. This validator checks whether an 8- or 9-digit IRD number is structurally correct using Inland Revenue’s published weighted modulus-11 check digit algorithm — entirely in your browser.

How it works

The final digit of an IRD number is a check digit derived from the rest. The validator:

Splits off the check digit and left-pads the base to 8 digits, requiring it to fall between 10,000,000 and 150,000,000.
Multiplies the 8 base digits by primary weights 3, 2, 7, 6, 5, 4, 3, 2, sums them, and computes the check digit as 11 − (sum mod 11), using 0 when the remainder is 0.
If that result is 10, it retries with secondary weights 7, 4, 3, 2, 5, 2, 7, 6. If still 10, the number is invalid.
Compares the computed check digit with the supplied one.

Example

For the valid test number 49091850, the base is 4909185. Padded to 04909185 and multiplied by the primary weights:

0×3 + 4×2 + 9×7 + 0×6 + 9×5 + 1×4 + 8×3 + 5×2 = 0 + 8 + 63 + 0 + 45 + 4 + 24 + 10 = 154

154 mod 11 = 0 (11 × 14 = 154), so the check digit is 0, which matches the supplied final digit of 49091850 — the number passes.

Privacy-first: every calculation runs in your browser. Nothing is uploaded, stored or sent to any server, and this tool does not query Inland Revenue or any other database.