$previous_date='20101202115755';
$current_date= date("YmdHis");
$day_difference=?????

$day = 60*60*24;

$now = time();
$target = strtotime('2010-12-24');

$diff = round(($target - $now) / $day);
echo $diff;

$prev = DateTime::createFromFormat("YmdHis", '20101202115755');
$curr = new DateTime();
$diff = $curr->diff($prev);
echo "Difference: ".$diff->days;

<?php
$previous_date="201012021157552";
$previous_date_as_time = mktime(
  substr($previous_date, 8, 2),
  substr($previous_date, 10, 2),
  substr($previous_date, 12, 2),
  substr($previous_date, 4, 2),
  substr($previous_date, 6, 2),
  substr($previous_date, 0, 4)
);

$days_between_dates = (time() - $previous_date_as_time) / 86400;

echo $days_between_dates;
?>

$d = strptime($previous_date, '%Y%m%d%H%M%S');
$prev_ts = mktime($d['tm_hour'], $d['tm_min'], $d['tm_sec'], $d['tm_mon'] + 1, $d['tm_mday'], $d['tm_year'] + 1900);

$diff = time() - $prev_ts;

$diff = floor($diff / (60*60*24)); // or round(), ceil() whatever fits best