This is how you define your form tag: <form>
So when submit is clicked, the form calls itself (the page it's on) and refreshes the screen.
You are never processing it, because it never executes "loan-calculator.php"
Even if you executed it by doing this ....
<form action="loan-calculator.php" method="post">
I think it would display the loan calculator but not the other page.
You're going to need in the least, some javascripting.
In fact, the whole loan calculator should be javascripting.
Better yet, JQuery.
If PHP is required to dynamically put numbers into the load "widget",
you'll end-up using AJAX, which is a combination of PHP and JQuery.
Scrap what you're using now and look at some of these:
http://www.google.com/search?q=php+a...or&btnG=Search
.