We can easily find date difference in php by using strtotime which convert two dates to unix time once convert we can manipulate easily by calculating the number of seconds between them.Its the easy way to calculate different time periods.

$date1 = "2013-03-20";
$date2 = "2015-06-30";

$diff = abs(strtotime($date2) - strtotime($date1));

$years = floor($diff / (365*60*60*24));
$months = floor(($diff - $years * 365*60*60*24) / (30*60*60*24));
$days = floor(($diff - $years * 365*60*60*24 - $months*30*60*60*24)/ (60*60*24));

printf("%d years, %d months, %d days\n", $years, $months, $days);

Another way is to get difference between two dates.

$date1 = new DateTime($date_1);
$date2 = new DateTime($date_2);
$interval = $date1->diff($date2);
echo "difference " . $interval->y . " years, " . $interval->m." months, ".$interval->d." days "; 

// shows the total amount of days 
echo "difference " . $interval->days . " days ";