Omocodia in Italian Tax Code
When two people have the same Tax Code: causes, solutions and how to recognize it
What is Omocodia?
Omocodia ("same code") occurs when two or more different people, applying the standard calculation algorithm, obtain the same Tax Code. This phenomenon, although rare, can happen when people share:
- Same surname (or consonants/vowels producing the same 3 letters)
- Same first name (or consonants/vowels producing the same 3 letters)
- Same birth date (day, month and year)
- Same birthplace (municipality or foreign country)
- Same gender
⚠️ Classic example: twin brothers with names producing the same 3 letters (e.g. MARCO and MIRCO both produce MRC).
How Omocodia Resolution Works
When the Revenue Agency detects an omocodia case, it modifies one or more numerical characters of the Tax Code, replacing them with letters according to a predefined table. The substitution occurs progressively, starting from the last numerical digit (position 15) and proceeding leftward.
The positions that can be modified are: 7th character (year), 10th-11th (day), 13th-14th-15th (municipality code).
Digit-Letter Substitution Table
The Revenue Agency uses this table to replace digits with letters in omocodia cases:
| Digit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|---|
| Letter | L | M | N | P | Q | R | S | T | U | V |
Practical Omocodia Example
Suppose two people have identical base Tax Codes. Here's how the Revenue Agency resolves the conflict:
Original code (1st level):
RSSMRA85C15H501R
1st omocodia level (last digit):
RSSMRA85C15H50MX
1 → M (CIN recalculated)
2nd omocodia level (second to last):
RSSMRA85C15H5LMY
0 → L (CIN recalculated)
Omocodia Levels
There are up to 127 possible omocodia combinations for the same base tax code. Levels are assigned progressively:
- Level 1: Substitution of digit at position 15
- Level 2: Substitution of digits at positions 14-15
- Level 3: Substitution of digits at positions 13-14-15
And so on, up to replacing all 7 available digits.
How to Recognize a Code with Omocodia
A Tax Code with omocodia has letters instead of digits in positions that normally contain numbers:
- •Letters L, M, N, P, Q, R, S, T, U, V instead of numbers 0-9
- •In positions 7 (year), 10-11 (day), 13-14-15 (municipality code)
- •The check character (CIN) will be different from the base code
💡 Important Information
- •Only the Revenue Agency can officially assign tax codes with omocodia
- •Our verifier automatically recognizes codes with omocodia
- •A code with omocodia is perfectly valid and legal
- •You cannot voluntarily request a code with omocodia
- •Omocodia is resolved at the time of the first CF request
Frequently Asked Questions about Omocodia
Is omocodia an error?
No, omocodia is not an error. It's a normal situation that the Revenue Agency manages automatically to ensure the uniqueness of each Tax Code.
Can I have problems with an omocodia CF?
No, a Tax Code with omocodia is perfectly valid. It might only cause confusion in automated systems that don't recognize it, but it's legally equivalent.
How do I know if I have an omocodia CF?
Use our verification tool: enter your CF and the system will tell you if it has omocodia and what level.
Verify your Tax Code
Our tool automatically recognizes if a code has omocodia