$first_next_month = date ("Y-m-d", mktime (0,0,0,date("m")+1, 15, date("Y")));
echo "Next month on the 15th: ".$first_next_month."<P>\n";
$five_next_month = date ("Y-m-d", mktime (0,0,0,date("m")+5, 15, date("Y")));
echo "5 months later: ".$five_next_month."<P>\n";
Thanks for every ones help.
Adam