<?php
// Solution 1
$date1 = new DateTime("2010-07-06");
$date2 = new DateTime("2010-07-09");
$diff = $date2->diff($date1)->format("%a");
echo $diff;

// Solution 2
$debut = strtotime('2010-01-25');
$fin = strtotime('2010-02-20');
$dif = ceil(abs($fin - $debut) / 86400);
echo $dif;

// Solution 3
$datetime1 = new DateTime("2010-06-20");
$datetime2 = new DateTime("2011-06-22");
$difference = $datetime1->diff($datetime2);
echo 'Difference: '.$difference->y.' Annees, ' 
                   .$difference->m.' Mois, ' 
                   .$difference->d.' Jours';

?>