Chinese ID Numbers: Structure, Dates and Check Characters

A Chinese identity number can have eighteen characters and still contain an impossible date or an incorrect check digit. Even when all those checks pass, a local calculator has not confirmed the holder’s identity. Keep number structure, historical address information and identity verification as separate questions.

The eighteen-character citizen identification number described here follows GB 11643-1999. It is the format used by ChinaClue’s Chinese ID checker. A passport, a different travel document or a legacy fifteen-digit entry needs its own handling; do not add digits merely to make it fit this form.

Read the four parts without changing the record

Read the number from left to right: six digits for the address code, eight for the birth date, three for the sequence and one final check character. The birth date uses year, month and day without separators. The first seventeen positions are decimal digits. The final character can be a digit or X; X represents the check value ten, not an unknown digit.

The standard’s published teaching example is 11010519491231002X. Split it as 110105 | 19491231 | 002 | X. That shows the address-code field, 31 December 1949, sequence 002 and the final check character. It is an example for understanding the structure, not a personal record to submit in an application.

The sequence is assigned within the address-code area for people with the same birth date. Its odd or even value encodes the male or female classification in the numbering rule. It is not the person’s age, household size or a counter you can use to infer how many people live in the district. A parsed field explains the number; it does not authorize conclusions beyond that coding rule.

The standard’s teaching example splits into address code 110105, birth date 19491231, sequence 002 and check character X: 6 + 8 + 3 + 1 characters.

Check the date independently of the final character

The eight birth-date digits must form a real Gregorian date. A month of 13 is invalid, and February does not always have the same number of days. For example, 2000-02-29 exists because 2000 is divisible by 400, while 1900-02-29 and 2026-02-29 do not. The tool also rejects a birth date later than today in Beijing.

The check digit is a separate calculation over the first seventeen digits. An invented string with a bad date can still be given a mathematically matching final character. Conversely, a real-looking date does not rescue a mistyped final character. Read each result separately rather than treating any one green result as approval of the whole entry.

When a date check fails, compare the original document before editing the data. A transposed day and month, a missing zero or a spreadsheet conversion can cause different problems. Do not assume a foreign date order applies inside this Chinese identifier: the encoded date is year–month–day.

Understand the X check character

The calculation uses seventeen fixed weights. From the left, they are 7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2. Multiply each of the first seventeen digits by its corresponding weight and add the results. Divide the sum by eleven and use the remainder to select the final character.

For the standard’s example, the weighted sum is 167 and the remainder is 2. The remainder-to-character mapping for remainders 0 through 10 is 1, 0, X, 9, 8, 7, 6, 5, 4, 3, 2. Remainder 2 therefore produces X. This is why replacing X with 0, 10 or a multiplication symbol changes the number.

ChinaClue accepts a lowercase x and normalizes fullwidth input for this check, while preserving the underlying identifier’s intended characters. If the tool reports a different expected check character, use it as a clue to a transcription problem. Do not simply replace the last character: the error could be earlier in the number.

Interpret the address code with its history

The six-digit address field follows administrative-division coding for the registered household location specified by the numbering rule. It is not a postal code, street address or live-location indicator. A person may live elsewhere; the number alone cannot tell you their present home or where they were physically born.

ChinaClue looks up the field in a historical 1981–2025 division dataset. A code absent from the latest year may still have a historical record. Do not replace a retired district code with its modern successor inside an identity number. That would alter the identifier and its check digit, not update a contact address.

The encoded birth year is not evidence of when the number was assigned. Do not choose a division-code year solely from the date of birth. Likewise, “not found” in this fixed dataset is a lookup result, not proof that the holder or document is invalid. Keep that finding separate from the number’s format and arithmetic checks.

Keep spreadsheet handling and verification separate

Store the complete value as text before importing it into a spreadsheet. Numeric cells can lose precision in an eighteen-digit value, while a number ending in X may behave differently from an all-numeric one. Changing a damaged numeric cell to text afterward does not restore digits already changed; return to the original document or export.

Use the checker to identify the failed layer: character format, birth date, sequence format, final check character or historical address lookup. Preserve the source value and document the correction you actually confirmed. Share a masked example when asking someone to diagnose formatting; the full identifier is normally unnecessary for explaining a spreadsheet problem.

A complete pass means the supplied text is consistent with the tested rules and available lookup data. It does not establish that the number was issued, that the document is genuine or that the person presenting it is the holder. Any service that requires identity verification must use its own authorized verification process.