$re = '/^\d{4}-(0\d|1[0-2])-([0-2]\d|3[0-2])(T(([01]\d|2[0-4]):([0-5]\d)(:[0-5]\d([\.,]\d+)?)?|([01]\d|2[0-4])(:[0-5]\d([\.,]\d+)?)?|([01]\d|2[0-4])([\.,]\d+)?))?([+-]\d\d(:[0-5]\d)?|Z)?$/';
$str = '2016-03-12T14:13:12.1209182451+03:00';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php