What is the China Resident Identity Card number?

It is the 18-character identifier on the second-generation Resident Identity Card (第二代居民身份证) issued to all Chinese citizens under the standard GB 11643-1999. The number encodes the holder's registration address, date of birth, and gender, and ends with a check character computed by the ISO 7064 MOD 11-2 algorithm.

How does the ISO 7064 MOD 11-2 check character work?

Each of the first 17 digits is multiplied by a fixed weight. The weights are derived from 2^(17-i) mod 11 for positions i = 0..16, giving [7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2]. The products are summed, the sum is taken modulo 11, and the remainder indexes into the string "10X98765432" to yield the check character. When the remainder is 2 the check character is X (representing the value 10, which cannot fit in one digit).

What does each segment of the 18-digit ID encode?

Digits 1–6 are the address code: the first two identify the province, the next two the prefecture, and the last two the county, all per GB/T 2260. Digits 7–14 are the date of birth in YYYYMMDD format. Digits 15–17 are a sequence number assigned within that area and birth date, with the 17th digit also encoding gender. Digit 18 is the check character.

How is gender encoded?

The 17th digit (third digit of the three-digit sequence number at positions 15–17) encodes gender by parity. An odd value means male and an even value means female. The validator reads and displays this automatically.

Why can the last character be X instead of a digit?

The ISO 7064 MOD 11-2 algorithm produces a check value in the range 0–10. When the value is 10 a single character position cannot hold two digits, so the letter X is used as the conventional symbol for 10. An X in position 18 is therefore valid and common.

Does a valid result mean the ID is registered to a real person?

No. This tool checks only structural and algorithmic correctness — the same checks a form-validation library would run. A passing result confirms that the number is internally consistent, but it cannot tell you whether it was ever assigned, who holds it, or whether it is currently active. Only authoritative MPS databases can confirm real-world registration.

Is my ID number sent anywhere?

No. This is a privacy-first tool. Every calculation — the checksum arithmetic, the province lookup, and the date parsing — runs in your browser. Nothing is ever transmitted to a server or stored.

China Resident ID Validator

The China Resident Identity Card number (居民身份证号码, standard GB 11643-1999) is the primary national identifier for Chinese citizens. This validator checks every structural rule defined in the standard, verifies the ISO 7064 MOD 11-2 check character, and decodes the province, date of birth, and gender that are embedded in the number — all in your browser, with no data uploaded anywhere.

How it works

The 18 characters of a second-generation Resident ID follow a fixed layout:

Positions	Segment	Meaning
1–2	Province	Two-digit code per GB/T 2260 (e.g. 11 = Beijing)
3–4	Prefecture	Sub-division of the province
5–6	County	Sub-division of the prefecture
7–10	Birth year	Four-digit year YYYY
11–12	Birth month	Two-digit month MM
13–14	Birth day	Two-digit day DD
15–17	Sequence	Unique within area + birth date; 17th digit encodes gender
18	Check char	ISO 7064 MOD 11-2 value — a digit 0–9 or the letter X

The validator applies six rules in sequence and marks each as pass or fail:

Length — exactly 18 characters after stripping spaces and hyphens.
Character set — positions 1–17 are decimal digits; position 18 is a digit or X.
Province code — the first two digits match the official GB/T 2260 division registry.
Birth date — digits 7–14 form a real calendar date (including month-length and leap-year checks) that is not in the future.
Sequence number — digits 15–17 are not the reserved value 000.
ISO 7064 MOD 11-2 check character — the recomputed check value equals the 18th character.

How the check character is computed

The algorithm multiplies each of the 17 data digits by a fixed weight, sums the products, takes the remainder modulo 11, and maps the result to a character:

weights = [7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2]

sum = d₁×7 + d₂×9 + d₃×10 + … + d₁₇×2

check = "10X98765432"[sum mod 11]

The lookup string "10X98765432" maps each possible remainder (0–10) to its check character. Remainder 2 produces X because the value 10 cannot be represented in a single decimal digit; X is the conventional ISO symbol for that case.

Worked example

The following number is obviously fictitious (sequential area code, round birth date, low sequence) and is provided solely to illustrate the structure:

1 1 0 1 0 1  1 9 9 0 0 3 0 7  0 0 3  8
└─────┬─────┘ └──────┬──────┘ └─┬─┘  └── check char
   address         birth       seq

110101199003070038

Province 11 → Beijing (北京)
Address code 110101
Date of birth 19900307 → 7 March 1990
Sequence 003; gender digit 3 (odd) → Male (男)
Weighted sum = 158, remainder 158 mod 11 = 4 → check char "10X98765432"[4] = 8 ✓

You can paste 110101199003070038 directly into the tool above to see the full step-by-step breakdown. Do not use this number for any real purpose — it is a structural demonstration only.

Formula note

The weight sequence [7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2] is not arbitrary: each weight equals 2^(17−i) mod 11 where i is the zero-based position index. Because 11 is prime the powers of 2 cycle with period 10, which is why the sequence repeats at positions 10–16. The mapping table "10X98765432" satisfies the MOD 11-2 property that re-appending the check character to the original number and running the same algorithm on all 18 digits always yields a fixed value (1 for this variant), making the algorithm self-checking.