<script>
// calculates the payments and updates for fields to
// display the result
function calcpayment() {
   var amt = document.frm.amt.value;
   var ir = document.frm.ir.value / 1200;
   var term = document.frm.term.value * 12;
   var total=1;

   for (i=0;i<term;i++) {
      total = total * (1 + ir);
   }
   mp = amt * ir / ( 1 - (1/total));

  // use Math object to chop all numbers after 2 digits
  document.frm.payment.value = Math.round(mp*100)/100;
  document.frm.total.value = Math.round(mp * term *100)/100 ;
}
</script>

<h2 style="text-align: center; color: black">Javascript Calculator</h2>
<hr/>
<center>
<form name="frm">
<table bgcolor="black" cellpadding="2"><tr><td>
<table bgcolor="wheat" cellspacing="10">
<tr>
  <td>Mortgage amount</td>
  <td><input type="text" name="amt" /></td>
</tr>

<tr>
  <td>Yearly interest rate</td>
  <td><input type="text" name="ir" /></td>
</tr>

<tr>
  <td>Term (in years)</td>
  <td><input type="text" name="term" /></td>
</tr>
<tr><td colspan="2"><hr/></td></tr>
 <tr>
  <td>Monthly payment:</td>
  <td><input type="text" name="payment" /></td>
</tr>

 <tr>
  <td>Total payments:</td>
  <td><input type="text" name="total" /></td>
</tr>
<tr >
<td colspan="2" width="100%">
<input type="button" value="Press to calculate monthly payment"
  onclick="calcpayment();" />
</td></tr>
</table>
</td></tr></table>
</form>
</center>