PHP Function for Validating Chinese ID Card Numbers

Chinese citizen ID numbers consist of a 17‑digit body code and a final checksum digit. The body code is composed of a six‑digit address code, an eight‑digit birthdate (YYYYMMDD), a three‑digit sequence code (odd for males, even for females), and the checksum digit.

The validation process includes:

Verifying the overall format with regular expressions for 15‑digit and 18‑digit IDs.

Extracting and checking the birthdate part using strtotime to ensure it represents a real date.

For 18‑digit IDs, calculating the checksum according to ISO 7064:1983.MOD 11‑2, where the weighting factors are 7 9 10 5 8 4 2 1 6 3 7 9 10 5 8 4 2 and the possible check characters are 0‑9 and X.

The following PHP function implements these steps:

<?php
function is_idcard($id)
{
    $id = strtoupper($id);
    $regx = "/(^\d{15}$)|(^\d{17}([0-9]|X)$)/";
    $arr_split = array();
    if (!preg_match($regx, $id)) {
        return FALSE;
    }
    // 15‑digit handling
    if (15 == strlen($id)) {
        $regx = "/^(\d{6})(\d{2})(\d{2})(\d{2})(\d{3})$/";
        @preg_match($regx, $id, $arr_split);
        $dtm_birth = "19".$arr_split[2]."/".$arr_split[3]."/".$arr_split[4];
        if (!strtotime($dtm_birth)) {
            return FALSE;
        } else {
            return TRUE;
        }
    } else {
        // 18‑digit handling
        $regx = "/^(\d{6})(\d{4})(\d{2})(\d{2})(\d{3})([0-9]|X)$/";
        @preg_match($regx, $id, $arr_split);
        $dtm_birth = $arr_split[2]."/".$arr_split[3]."/".$arr_split[4];
        if (!strtotime($dtm_birth)) {
            return FALSE;
        }
        // checksum calculation
        $arr_int = array(7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2);
        $arr_ch  = array('1','0','X','9','8','7','6','5','4','3','2');
        $sign = 0;
        for ($i = 0; $i < 17; $i++) {
            $b = (int)$id{$i};
            $w = $arr_int[$i];
            $sign += $b * $w;
        }
        $n = $sign % 11;
        $val_num = $arr_ch[$n];
        if ($val_num != substr($id, 17, 1)) {
            return FALSE;
        } else {
            return TRUE;
        }
    }
}
?>

Example usage:

<?php
$rest = is_idcard('123456789012345678');
var_dump($rest); // bool(false)
?>