[Sebastian]

i am usually good with math
if this doesn't work then maybe Xenon can give it a crack.

PHP Code:

$qbpermonth += $userinfo[quads] + $userinfo[bikes];
$qbtime = (time() - $userinfo[joindate]) / 2592000; // Days Joined
  if ($qbtime < 1) { // User has been a member for less than one day.
    $qbpermonth = $qbpermonth;
  } else {
    $qbpermonth = sprintf("%.2f",($qbpermonth / $qbtime));
  }