Anatomy of an Icelandic Kennitala ID & Modulus 11 Checksum
Every resident and registered legal entity in Iceland is assigned a unique 10-digit national identification number called a Kennitala (issued by Þjóðskrá Íslands for natural persons and by Skatturinn / Fyrirtækjaskrá for corporations). Digits 1–6 encode the date of birth or incorporation (DDMMYY), digits 7–8 are a serial number (20–99 for individuals), digit 9 is the Modulus 11 check digit, and digit 10 indicates the century (9 for 1900–1999, 0 for 2000–2099).
| Digit Position | 1 (D) | 2 (D) | 3 (M) | 4 (M) | 5 (Y) | 6 (Y) | 7 (S) | 8 (S) |
|---|---|---|---|---|---|---|---|---|
| Modulus 11 Weight | 3 | 2 | 7 | 6 | 5 | 4 | 3 | 2 |
👤 Natural Persons (Digits 01–31)
For individuals, the first two digits are between 01 and 31, representing the calendar day of birth. Serial digits 7–8 always start at 20 or higher.
🏢 Legal Entities & Companies (41–71)
For corporations (ehf., hf., branches, NGOs), 40 is added to the registration day. A company incorporated on May 15 starts with 5505.
🔍 Corporate Registry & VAT Link
Every business VAT registration number (5–6 digits) is tied to a legal Kennitala in the Iceland Company Registry (Fyrirtækjaskrá).
Mathematical Formula, Worked Verification Example & System IDs (Kerfiskennitala)
To validate the 9th digit (check digit) of an Icelandic Kennitala, multiply each of the first eight digits by its corresponding positional weight from the vector [3, 2, 7, 6, 5, 4, 3, 2] and sum the products to obtain S. Next, compute the modulo remainder R = S mod 11. If R === 0, the check digit is 0. If R is between 2 and 10, the check digit is 11 − R. If R === 1, the result would be 10 (which requires two digits), so that specific serial combination is invalid and skipped by the national registry generator.
Worked Calculation Example (Company Kennitala 550520-0280):
• Digits 1–8: 5, 5, 0, 5, 2, 0, 0, 2 (Incorporation day: 55 − 40 = May 15, 2020).
• Weighted sum: (5×3) + (5×2) + (0×7) + (5×6) + (2×5) + (0×4) + (0×3) + (2×2) = 15 + 10 + 0 + 30 + 10 + 0 + 0 + 4 = 69.
• Modulo 11 step: 69 mod 11 = 3 (since 6 × 11 = 66). Therefore, the 9th check digit is 11 − 3 = 8, and the 10th digit is 0 (21st century), confirming that 550520-0280 is mathematically valid.
System IDs (Kerfiskennitala) & B2B Invoice Compliance: Foreign nationals working in Iceland temporarily (less than 3–6 months) or non-resident entities with tax obligations are issued a temporary Kerfiskennitala by Registers Iceland (often starting with digit 8 or 9) for payroll withholding and banking. Under Ministry Regulation No. 505/2013 and VAT Act No. 50/1988, validating both the supplier's Kennitala and 5–6 digit VAT number before paying a domestic B2B invoice is mandatory to safeguard input VAT deductions.