how to compare date format in php code example

Example 1: php compare two dates

$today = date("Y-m-d");
$expire = $row->expireDate; //from database

$today_time = strtotime($today);
$expire_time = strtotime($expire);

if ($expire_time < $today_time) { /* do Something */ }

Example 2: php compare dates

$date1 = "2021-01-15";
$date2 = "2021-01-18";

if ($date1 < $date2) {
 	echo "$date1 is earlier than $date2";
} else {
	echo "$date1 is later than $date2";
}