<?php
function dateDifference($start_date, $end_date)
{
// calulating the difference in timestamps
$diff = strtotime($start_date) - strtotime($end_date);

// 1 day = 24 hours
// 24 * 60 * 60 = 86400 seconds
return ceil(abs($diff / 86400));
}

// start date
$start_date = "2016-01-02";

// end date
$end_date = "2016-01-21";

// call dateDifference() function to find the number of days between two dates
$dateDiff = dateDifference($start_date, $end_date);

echo "Difference between two dates: " . $dateDiff . " Days ";
?>