Home IRD number New Zealand
New Zealand IRD number validator
How the IRD number format works
- Format
- 8 or 9 digits, the last being a mod-11 check digit
- Example
- 49091850
Things to watch for
- IRD numbers are often printed with hyphens (e.g. 049-091-850) — this validator strips those automatically before checking
- Format + mod-11 checksum only — a pass doesn't confirm the IRD number is currently active or registered to anyone
- An IRD number is sensitive tax-ID data — this validator runs entirely in your browser and never sends or stores what you type
^[0-9]{8,9}$A New Zealand IRD number is the tax identifier Inland Revenue assigns to individuals and organisations for income tax, GST, and other tax dealings. It’s 8 or 9 digits long, with the final digit acting as a check digit over the rest. It’s commonly printed with hyphens grouping the digits (for example 049-091-850), which this validator strips automatically before checking.
How the check digit is derived
The check digit comes from a weighted sum: the base number is left-padded to 8 digits if it’s only 7, each digit is multiplied by a fixed weight, and the results are summed and reduced modulo 11. Most of the time that’s the whole story — but if the calculation lands on 10, which can’t be written as a single digit, Inland Revenue’s own specification switches to a second, different set of weights and tries again, only rejecting the number if that also produces 10. That two-tier fallback is unusual among mod-11 check digits, and it’s why a correct validator has to implement both weight sets rather than just one to agree with genuine IRD numbers.
What this check confirms
A pass here means the check digit matches the calculation Inland Revenue’s specification defines — nothing about whether the number is currently assigned, active, or linked to a real taxpayer. That confirmation only comes from Inland Revenue itself, not a client-side arithmetic check. Because an IRD number is sensitive tax data, everything runs locally in your browser, with nothing sent or stored.
Content last reviewed 2026-08-09.
IRD number FAQ
How many digits does an IRD number have?
8 or 9 digits, the last of which is a check digit. IRD numbers are often printed with hyphens for readability (e.g. 049-091-850) — this validator strips those automatically, so pasting the number exactly as printed still works.
How is the IRD check digit calculated?
The remaining 7 or 8 digits are left-padded to 8 and each multiplied by a fixed weight, then summed and reduced modulo 11 to get a candidate check digit. If that calculation produces 10 — not a valid single digit — Inland Revenue's specification falls back to a second set of weights and tries again; if that also produces 10, the number is invalid.
Does a valid IRD number mean it's registered to someone?
No. This only confirms the check digit is mathematically correct for the digits before it — it can't confirm Inland Revenue has actually issued that number or that it's active on anyone's account. Because an IRD number is sensitive tax-ID, this validator runs entirely in your browser and never sends or stores what you type.