A kennitala (plural kennitalur) is Iceland's unique national identifier, assigned to every individual at birth and to every legal entity at registration. It is 10 digits long and encodes the date of birth or registration date, a random two-digit serial, a century indicator, and a Lund check digit. Individuals retain the same kennitala for life; companies keep theirs until dissolution.

How is the kennitala check digit calculated?

The Lund algorithm applies the weight sequence 3, 2, 7, 6, 5, 4, 3, 2 to the first eight digits. The weighted values are summed and the remainder mod 11 is taken. If the remainder is 0, the check digit is 0. If the remainder is 10, the combination is inherently invalid and no valid kennitala can end with those eight digits. Otherwise the check digit is 11 minus the remainder. The ninth digit (century indicator) is not included in the sum.

How do I tell whether a kennitala belongs to a person or a company?

Look at the first two digits (the day field). For individuals the day field is 01 through 31, matching the actual day of birth. For legal entities the real registration day has 40 added to it, so the day field runs from 41 (day 1) through 71 (day 31). This tool detects and labels the holder type automatically.

What does the century indicator (the 9th digit) mean?

The ninth digit encodes the century of the birth or registration year. The digit 9 means 1900s (born or registered 1900–1999), the digit 0 means 2000s (2000–2099), and the digit 8 means 1800s (1800–1899). Any other value is invalid.

What does a "Valid" result actually mean?

A green Valid result means the number satisfies all five published structural rules — correct length, a plausible day field, a valid month, a recognised century indicator, and a correct Lund check digit. It does not confirm that the kennitala is currently active, assigned to a living person, or registered in any government database. Only Iceland's Registers Iceland (Þjóðskrá) can confirm registration status.

Why might a structurally correct kennitala be flagged invalid?

The most common cause is a single transposed or misread digit breaking the check digit. The day field being 00 or above 71, the month being 00 or above 12, or a century indicator other than 0, 8, or 9 also fail immediately. A less obvious cause is a digit combination where the weighted sum mod 11 equals 10 — those eight digits cannot produce any valid kennitala regardless of what check digit is appended.

Iceland Kennitala Validator

Iceland’s kennitala (plural: kennitalur) is the national identifier issued to every person born in or moving to Iceland, and to every legally registered company or organisation. Unlike many national IDs, it encodes meaningful information directly into its digits — the holder’s date of birth (or a company’s registration date), a century marker, and a mathematically verified check digit. This validator implements the full official specification so you can catch typos in forms, onboarding pipelines, and data imports before they reach a live system.

The tool works entirely in your browser. Nothing you enter is sent over the network.

How it works

A kennitala is always 10 digits (a hyphen after the sixth digit is cosmetic and ignored). The positions carry the following meaning:

Positions	Field	Notes
1–2	Day (DD)	01–31 for persons; 41–71 for legal entities (real day + 40)
3–4	Month (MM)	01–12
5–6	Year (YY)	Last two digits of the year
7–8	Serial (NN)	Random, ensures uniqueness for the same date
9	Century indicator (K)	8 = 1800s, 9 = 1900s, 0 = 2000s
10	Check digit (C)	Lund weighted mod-11 checksum over positions 1–8

The Lund check-digit algorithm

The check digit is calculated over the first eight digits only (the century indicator at position 9 is excluded). Weights 3, 2, 7, 6, 5, 4, 3, 2 are applied in order:

sum = d₁×3 + d₂×2 + d₃×7 + d₄×6 + d₅×5 + d₆×4 + d₇×3 + d₈×2

Then:

If sum mod 11 = 0 → check digit = 0
If sum mod 11 = 10 → no valid kennitala exists for those eight digits
Otherwise → check digit = 11 − (sum mod 11)

Identifying persons vs. legal entities

The first two digits reveal the holder type. For an individual, the day field is 01–31. For a company or other legal entity, 40 is added to the real registration day, so the field reads 41–71. The validator detects this automatically and labels the result accordingly.

Worked example

Take the obviously-fake kennitala 150385-0098 (do not use as real data):

Step	Calculation
Digits 1–8	1, 5, 0, 3, 8, 5, 0, 0
Weighted sum	1×3 + 5×2 + 0×7 + 3×6 + 8×5 + 5×4 + 0×3 + 0×2 = 3+10+0+18+40+20+0+0 = 91
Remainder	91 mod 11 = 3
Check digit	11 − 3 = 8 ✓ (matches position 10)
Century indicator	K = 9 → 1900s
Full decoded date	Day 15, Month 03, Year 85 → 15 March 1985
Holder type	Day field 15 (≤ 31) → Person

For a company example, 470605-0006 represents an entity registered on day 7 (= 47 − 40) of June 2005. The K digit is 0, indicating the 2000s.

Formula note

The Lund mod-11 scheme intentionally excludes the century indicator from the weighted sum. This means the same eight-digit prefix with different K values (8, 9, 0) always produces the same check digit — the century is independently verified by range checks, not by the checksum. The consequence is that any input where sum mod 11 = 10 has no valid check digit at all, making that 8-digit combination structurally impossible regardless of what is appended.

Every calculation happens client-side — your kennitala is never transmitted anywhere.