How to compare two dates using PHP

First we need to convert the two dates to UNIX Timestamps using the PHP function strtotime

Then we can compare the two dates in anyway we wish, in the example below I’m checking that the first date is older than the second date 

$date1 = '1999-10-11';
$date2 = '2010-10-11';
 
$firstDate = strtotime($date1);
$secondDate = strtotime($date2);
 
if($firstDate < $secondDate){
     echo 'First date is older';
}else{
     echo 'Second date is older';
}