What is the structure of a Chinese ID number?

An 18-digit resident identity card encodes a 6-digit administrative-division (address) code, an 8-digit birthdate as YYYYMMDD, a 3-digit sequence number, and a final check digit. The card was extended from 15 to 18 digits in 1999.

How is the check digit calculated?

Each of the first 17 digits is multiplied by a fixed weight, the products are summed and reduced modulo 11. The remainder maps through the table 1,0,X,9,8,7,6,5,4,3,2 to give the check character, which is why X can appear in the last position.

Why is the last character sometimes X?

The check digit is computed modulo 11, so it can take eleven values 0-10. The value 10 cannot be written as a single digit, so it is represented by the Roman numeral X. About one in eleven valid cards ends in X.

Can I tell someone's sex from the number?

Yes. The 17th digit (the third digit of the sequence code) is odd for males and even for females. The tool reads this digit, but treat the result as informational only.

Does a valid number mean the person is real?

No. A valid check digit only proves the number is internally consistent and has a plausible birthdate and province code. It does not confirm that the card or individual exists. Treat ID numbers as sensitive personal data.

China Resident ID Card Validator

A Chinese resident identity card (居民身份证) carries an 18-digit number used across KYC, HR and banking systems in China. This validator confirms the format and the official check digit, and decodes the embedded province, birthdate and sex, all entirely in your browser so the sensitive number never leaves your device.

How it works

The 18 characters break down as:

Positions 1–6 — administrative-division (address) code; the first two digits indicate the province.
Positions 7–14 — date of birth as YYYYMMDD.
Positions 15–17 — sequence code; the 17th digit is odd for males, even for females.
Position 18 — the ISO 7064 MOD 11,2 check digit.

To compute the check digit, multiply the first 17 digits by the weights 7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2, sum the products, and take the result modulo 11. The remainder maps through the table 1,0,X,9,8,7,6,5,4,3,2 to give the final character — which is why a valid card can end in X (representing the value 10).

Notes

The tool also checks that the embedded birthdate is a real calendar date and flags an unknown province prefix. A passing checksum proves only internal consistency, not that the card or person exists. Chinese ID numbers are sensitive personal data, so this tool performs no network calls.