What is a Finnish henkilötunnus (HETU)?

A HETU is the Finnish national personal identity code issued by the Digital and Population Data Services Agency (DVV). Every Finnish resident and citizen has one. It is used for health records, tax, banking, and most government services. The 11-character code encodes date of birth, a century marker, an individual serial number, and a control character.

How is the HETU control character calculated?

Take the six-digit date block (DDMMYY) and the three-digit individual number (ZZZ), concatenate them into a 9-digit integer, divide by 31, and take the remainder (0–30). Look up that index in the official 31-character table: 0123456789ABCDEFHJKLMNPRSTUVWXY. The letters I, O, Q, and Z are intentionally absent so the character cannot be misread as a digit.

What do the century markers +, -, and A mean?

The single character between the date block and the individual number encodes the century of birth: + means 1800–1899, - means 1900–1999, and A means 2000–2099. Future markers (B, C, D, E, F) are reserved in the DVV specification for years 2100 and beyond.

How does HETU encode gender?

The three-digit individual number (ZZZ) is odd for males and even for females. For example, individual number 007 indicates male and 008 indicates female. Numbers 900–999 are reserved for test identities used in software development and do not correspond to real people.

Does a valid HETU confirm the person exists?

No. The validator only checks internal consistency — that the date is a real calendar date, the century marker is recognised, and the control character matches the mod-31 calculation. It does not query any Finnish government database and cannot confirm whether the number was actually issued to a living person.

Is the HETU ever printed on official documents?

Yes. The HETU appears on the Finnish identity card (henkilökortti), passport data page, Kela (social insurance) card, and many official letters. It is considered sensitive personal data under Finnish law and the GDPR — treat it accordingly and never log or store HETUs unnecessarily.

Finland HETU Validator

Finland HETU validator

The henkilötunnus (HETU) is Finland’s national personal identity code, issued to every resident by the Digital and Population Data Services Agency (DVV, formerly VRK). It appears on identity cards, passports, healthcare records, tax returns, and bank accounts. The 11-character code packs four pieces of information into a compact, human-readable string: the holder’s date of birth, the century they were born in, a serial number that encodes gender, and a single control character that lets any application verify the code without contacting a server.

This tool implements the full official DVV validation algorithm so you can check whether a HETU is internally consistent, see exactly which step passes or fails, and extract the embedded birth date and gender — all without sending any data over the network.

How the format works

A HETU always has exactly 11 characters in this structure:

D D M M Y Y C Z Z Z Q

DDMMYY — day, month, and last two digits of birth year, all zero-padded.
C — century marker: + for 1800–1899, - for 1900–1999, A for 2000–2099.
ZZZ — three-digit individual number, 001–899 for real persons (900–999 reserved for test IDs). Odd = male, even = female.
Q — control character produced by the mod-31 algorithm described below.

The mod-31 control character algorithm

Strip the century marker and concatenate the remaining nine digits: DDMMYY + ZZZ.
Interpret the nine-digit string as an integer N.
Compute remainder = N mod 31. The result is a number from 0 to 30.
Look up remainder as an index into the 31-character table:

Index:  0  1  2  3  4  5  6  7  8  9
Chars:  0  1  2  3  4  5  6  7  8  9

Index: 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Chars:  A  B  C  D  E  F  H  J  K  L  M  N  P  R  S  T  U  V  W  X  Y

The letters I, O, Q, and Z are absent to avoid confusion with digits 1, 0, 9, and 2.

The final character of the HETU must equal the character at the computed index.

Example — an obviously fake HETU

Consider the fictional HETU 131052-308T:

Part	Value	Meaning
DD	13	Day 13
MM	10	October
YY	52	Year …52
C	`-`	Century 1900–1999, so born 1952
ZZZ	308	Even → female
Q	T	Control character to verify

Calculation: join the nine digits → 131052308. Compute 131052308 mod 31 = 25. Index 25 in the table is T. The given control character is T — match, so the code is valid.

This is a made-up number used only to demonstrate the algorithm. Never use it in any real system.

What the validator reports

Birth date — the full four-digit year reconstructed from the century marker.
Gender — derived from the parity of the individual number.
Test identity flag — raised when the individual number is 900–999.
Nine-digit base number and remainder — shows exactly how the mod-31 was computed.
Expected vs. given control character — the specific character from the lookup table compared to what was entered.

The validator runs every check locally. No HETU, partial input, or result is ever sent to a server.