I think the question says it all. I am not sure how to get the currentdate + 2 days. here was my attempt
//insert invoice table
$currentdate = getdate();
$duedate = getdate() + 2000;
$makeinvoice = mysql_query("INSERT INTO invoices (userid, hostid, price, ispaid, detecreated, duedate) VALUES ('$userid', '$prodid', '$initprice', '0', '$currentdate','$duedate' )",$conn);