Italian Codice Fiscale

What it covers

Returns a valid Italian Codice Fiscale with a correct check character. Constrain with `sex`, age/birth-date filters (year, month, and day are encoded), and the optional `surname`/`name` to encode. Contradictory combinations are rejected with a 400. Set `invalid=true` for a deliberately wrong check character.

The codice fiscale is Italy’s personal tax code: sixteen characters encoding a surname code, a name code, the birth year, month (as a letter), day (offset by 40 for women), a place-of-birth code, and a final check character. It is alphanumeric, not purely numeric — the check is over letters and digits alike.

How it’s calculated

The sixteenth character is a mod-26 check letter computed from the first fifteen, using separate odd- and even-position value tables.

Position 1 (odd): R → ODD table value
Position 2 (even): S → EVEN table value (S = 18)
… alternate ODD/EVEN across all 15 characters …
sum = Σ(odd-table values at positions 1,3,5,…) + Σ(even-table values at positions 2,4,6,…)
check = sum mod 26
map check: 0 → A, 1 → B, …, 25 → Z

Edge cases

• The day field encodes sex: for women, 40 is added to the birth day, so a woman born on the 3rd carries day 43. The two-digit day therefore ranges 01–31 for men and 41–71 for women.
• The month is a letter, not a number: A, B, C, D, E, H, L, M, P, R, S, T map to January…December (skipping letters that resemble digits).
• The check character is a letter A–Z, never a digit — it is the only field computed from all fifteen preceding characters.

Gotchas

• Odd and even positions use entirely different value tables, and “odd/even” is 1-indexed — the first character is an odd position. A validator that 0-indexes will swap the two tables and reject valid codes.
• Homocodia: when two people would collide, digits in the omocodia positions are replaced with letters. This generator produces the base (non-omocodic) form.