Estonia Isikukood validator
How the Isikukood format works
- Format
- 11 digits
- Example
- 36805280109
Things to watch for
- 11 digits validated with a two-pass weighted mod-11 check on the final digit — a second weight set is used when the first pass produces an undefined remainder
- The first digit encodes sex and century and the next 6 a date of birth — we validate format and checksum only, never the date, and never store what you enter
- Checksum only — a valid isikukood does not confirm the number is currently issued to a real person
^[0-9]{11}$An isikukood is Estonia’s 11-digit national identity number, issued to residents and citizens and used as the backbone of the country’s digital-government services — logging into state e-services, signing documents digitally, e-voting, and authenticating on the national ID card and Mobile-ID — alongside the everyday paperwork of banking, healthcare, and tax filing. Structurally it’s not a random string: the first digit encodes sex and century, the next six form a date of birth, three more digits are a serial number, and the eleventh is a check digit computed from the other ten.
That check digit is where this validator earns its keep. It’s produced by a two-pass weighted mod-11 calculation: a first weighted sum over the first ten digits, and — only on the minority of numbers where that sum’s remainder is undefined (10) — a second sum with a different set of weights. A single mistyped or transposed digit almost always breaks at least one of those passes, which is exactly the kind of typo this tool is built to catch before a form submission bounces back.
How this validator works
This tool confirms the input is 11 digits, then reruns the same two-pass weighted mod-11 calculation used to generate the eleventh digit, entirely in your browser. Nothing you enter — including the date of birth and sex it encodes — is sent to a server, logged, or stored.
What a pass doesn’t tell you
A matching check digit means the 11 digits are arithmetically consistent with each other, not that the isikukood was ever assigned by Estonia’s Population Register or is currently held by a real person. Only that register can confirm a specific number is genuinely on file.
Scope: this page covers isikukood format and checksum validation only — not identity or registration lookups, and never the embedded date of birth or sex.
Content last reviewed 2026-08-09.
Isikukood FAQ
What do the 11 digits of an Estonian isikukood encode?
The first digit encodes sex and century (so it distinguishes someone born in the 1800s, 1900s, or 2000s), the next six digits are a date of birth in YYMMDD form, three more digits form a serial number issued that day, and the eleventh digit is a calculated check digit.
Why does the isikukood checksum use two weight passes?
The first pass runs a weighted mod-11 sum using one set of multipliers. On most numbers that produces a usable remainder (0-9), which becomes the check digit directly. On the rare number where that remainder comes out to 10 — mathematically undefined as a single digit — the algorithm reruns the sum with a second set of weights instead of rejecting the number outright, and a remainder of 10 on that second pass falls back to a check digit of 0.
Does a valid isikukood confirm the person is registered in Estonia?
No. A matching check digit only confirms the 11 digits are internally consistent — it doesn't confirm the number was ever issued by Estonia's Population Register or belongs to a specific person. Only that register can confirm a specific isikukood is genuinely on file.