How does the female month rule work?

For women, 50 is added to the birth month, so a March birth shows 53. Slovakia and Czechia also use +20 and +70 offsets for extra serial capacity, so a single date can carry more than 999 people.

What is the modulo-11 check?

Birth numbers issued from 1954 are 10 digits and the whole number must be divisible by 11. A pre-1985 exception allowed a remainder of 10 to map to a final digit of 0, so the tool accepts that legacy case too.

Why are some numbers only 9 digits?

Birth numbers assigned before 1954 have only 9 digits and carry no check digit, so only the date and sex rules are validated for them. From 1954 onward a tenth control digit was added.

Is the Slovak rule the same as the Czech one?

Yes. Slovakia and the Czech Republic shared the same rodné číslo system as Czechoslovakia, so the date encoding, sex offset, and modulo-11 rules are identical across both countries.

Is my birth number sent anywhere?

No. The whole validation runs in your browser using JavaScript. The rodné číslo never leaves your device, which matters because it is sensitive personal data.

Slovakia Rodné číslo Validator

A rodné číslo (birth number) is the national identification number used in Slovakia, inherited from the shared Czechoslovak system and still identical to the Czech rule. It encodes a person’s date of birth and sex, plus a control digit for numbers issued from 1954 onward. This free validator checks all of those rules in your browser.

How it works

The number is YYMMDD followed by a serial:

A 9-digit number is pre-1954 and has no control digit. A 10-digit number has a control digit and must pass the modulo-11 test.
The first two digits are the year within the century. The next two are the month, with offsets: a plain month is male; +50 marks a female; +20 and +70 are extra-serial ranges used after capacity ran out (and +70 also marks female).
The day must be valid for the decoded month.
For 10-digit numbers, treat the whole thing as an integer and require it to be divisible by 11. A legacy pre-1985 exception lets a mod 11 of 10 map to a final digit of 0.

Example

Take 740104/0020. The date part 740104 decodes to 4 January 1974. The month 01 is below 13, so the person is male. As a 10-digit number, 7401040020 mod 11 = 0, so it is divisible by 11 and the control passes — the number is valid.

Notes

A valid result confirms the number is internally consistent and encodes a real date — it does not prove the number was actually issued to a living person. Because the rodné číslo is sensitive personal data, all processing here is local and nothing is uploaded.