- floor: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$today = date('m/d/Y');
$today = strtotime($today);
$finish = get_field('todate');
$finish = strtotime($finish);
//difference
$diff = $finish - $today;
$daysleft=floor($diff/(60*60*24));
echo "$daysleft days left";
?>