Guide
What is omocodia in the codice fiscale?
By Codice Fiscale Pro Team · Published on
What is omocodia?
Omocodia is the situation in which the calculation would give the same codice fiscale to two or more people, because surname, first name, date and place of birth produce the same characters. The code alone cannot tell every individual apart, as Money.it (in Italian) and Business Online (in Italian) explain.
How is omocodia resolved?
The Agenzia delle Entrate replaces one or more digits of the code with letters, starting from the rightmost digit, until the code becomes unique. It then recalculates the check letter. This is reported by Pmi.it and Fiscomania (both in Italian). According to Informazione Fiscale (in Italian), the Agenzia generates new unique codes and may summon the people concerned to sort out the records.
Which digits are replaced, and by which letters?
The replacement affects the seven digits in positions 7, 8, 10, 11, 13, 14 and 15. Each digit has a matching letter.
| Digit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|---|
| Letter | L | M | N | P | Q | R | S | T | U | V |
What does a code look like after each replacement?
Take the example code RSSMRA85T10H501O. Replacements run from position 15 towards the left, and the final letter is recalculated at each step. The codes below are built for illustration and were calculated with our engine.
| Step | Code | Digit replaced |
|---|---|---|
| 0 (base) | RSSMRA85T10H501O | none |
| 1 | RSSMRA85T10H50MG | position 15: 1 becomes M |
| 2 | RSSMRA85T10H5LMR | position 14: 0 becomes L |
| 3 | RSSMRA85T10HRLMM | position 13: 5 becomes R |
| 4 | RSSMRA85T1LHRLMP | position 11: 0 becomes L |
| 5 | RSSMRA85TMLHRLMA | position 10: 1 becomes M |
| 6 | RSSMRA8RTMLHRLMM | position 8: 5 becomes R |
| 7 | RSSMRAURTMLHRLMJ | position 7: 8 becomes U |
What happens to foreign nationals?
For foreign nationals the Agenzia delle Entrate brochure "Codice fiscale stranieri" (in Italian) describes the procedure. If two or more people have details that generate the same code, the immigration desk or the police headquarters invites the person to an Agenzia office, which issues the definitive code after a check. A provisional code is valid in the meantime.
How do you recognise an omocodia code?
Look for letters in the seven positions that normally hold digits. Our decoder recognises these letters, rebuilds the original digits and recalculates the check letter. It accepts all 128 possible combinations of replacement, although the codes actually assigned follow the right-to-left order described above.
Can you calculate your own omocodia code?
No. An online calculation cannot know whether your code was modified, because it has no access to the tax registry. It can show you the base code. For the code in use, look at your health card or ask the Agenzia delle Entrate.
Sources
- Pmi.it and Fiscomania (Italian): replacement rule from the right.
- Informazione Fiscale (Italian): how the Agenzia resolves it.
- Agenzia delle Entrate (Italian): brochure "Codice fiscale stranieri", procedure for duplicates.
Frequently asked questions
What is omocodia in simple terms?
It is the case where two people would get the same codice fiscale because their details are identical. The Agenzia delle Entrate gives one or both of them a code with some digits replaced by letters.
Is a code with letters instead of digits wrong?
No. If the letters are among L, M, N, P, Q, R, S, T, U, V and sit in position 7, 8, 10, 11, 13, 14 or 15, the code can be a valid omocodia variant.
Can I find out by calculation whether I have an omocodia code?
No. A calculation gives the base code. To know which code was assigned to you, look at your health card or at documents from the Agenzia delle Entrate.
What should I do if I have an omocodia code?
Use the code that the Agenzia delle Entrate gave you, because it is the only valid one. If you are unsure which one to use, ask an office of the Agenzia.
Related guides
- How the Codice Fiscale Is Calculated | Codice Fiscale Pro: The rules for surname, first name, date, place and check letter, with worked examples.
- Formal Check vs Official Verification | Codice Fiscale Pro: What an independent site checks and what the Agenzia delle Entrate checks.
- When Can the Codice Fiscale Change? | Codice Fiscale Pro: Marriage, moving, corrected data, name or sex changes and omocodia: what changes the code and what does not.
- Common Codice Fiscale Mistakes and How to Avoid Them | Codice Fiscale Pro: The most frequent mistakes in hand calculation and online tools.