How does a rodné číslo encode the date and sex?

The first six digits are YYMMDD. For females, 50 is added to the month, so a month value above 50 (e.g. 56) means a female born in that month minus 50. An extra +20 can appear when all sequence numbers for a day were exhausted.

What is the modulo-11 check?

Numbers issued from 1954 onward have 10 digits, and the whole number must be divisible by 11. A historical pre-1985 exception allowed a final digit of 0 when the first nine digits left a remainder of 10 modulo 11.

Why do 9-digit numbers skip the modulo-11 check?

Numbers issued before 1954 have only 9 digits and predate the modulo-11 rule, so the tool validates their structure and encoded date but marks the modulo-11 check as not applicable.

Does a valid result identify a real person?

No. A valid result confirms the number is structurally correct with a plausible birth date and a passing checksum. It cannot confirm the number was actually issued to a real person.

Is my rodné číslo sent anywhere?

No. Validation runs entirely in your browser. This personal identifier never leaves your device, which matters for HR and healthcare data.

Czech Rodné číslo Validator

A rodné číslo (RC) is the national birth number issued to everyone in the Czech Republic (and historically Czechoslovakia). It encodes the date of birth and sex and, for modern numbers, carries a checksum. This free validator decodes those fields and runs the checks in your browser.

How it works

The number is read in segments:

The first six digits are the birth date in YYMMDD form.
For females, the month is offset by +50 (a month like 56 means June for a woman). A further +20 can be added when a day’s sequence numbers were exhausted; the tool subtracts these offsets to recover the real month.
The century is inferred from the length and year: 9-digit numbers are pre-1954, while 10-digit numbers pivot around year 54.
For 10-digit numbers (1954 onward), the whole number must be divisible by 11. A pre-1985 exception permitted a final digit of 0 when the first nine digits left a remainder of 10.

The tool shows the decoded date, the inferred sex, whether the date is plausible, and the modulo-11 result.

Notes

A valid result confirms structure, a plausible encoded date, and (for 10-digit numbers) the checksum. It does not prove the number was issued to a real person. Everything runs locally — the identifier never leaves your device.