- strtotime: documentation ( source)
<ul>
<?php
$values = array();
$values[] = array('example'=>'example1','date'=>'2016-12-25');
$values[] = array('example'=>'example2','date'=>'2016-12-26');
$values[] = array('example'=>'example3','date'=>'2016-12-28');
$values[] = array('example'=>'example4','date'=>'2016-12-30');
$previous = null;
foreach($values as $example){
echo "<li>".$example['example']." - ".$example['date'];
if ($previous !== null) {
$diff = strtotime($example['date'])-strtotime($previous);
echo " - ".($diff/(60*60*24));
}
$previous = $example['date'];
echo "</li>\n";
}
?>
</ul>