function calculatePayment(price)
{
	var downpayment = document.getElementById('downpayment').value;
	var term = document.getElementById('term').value;
	var rate = document.getElementById('rate').value;
	var payment = 0;
	var factor = 0;
	if (IsNumeric(downpayment) && IsNumeric(term) && IsNumeric(rate) && IsNumeric(price) )
	{
		rate = rate/1200;

		if (rate == 0)
		{
			payment = (price-downpayment) / term;
		}
		else
		{
			factor = Math.pow(1 + rate, term);
			payment = (price-downpayment) * ( rate / (1 - 1/factor) );
		}

		document.getElementById('estimatedPayment').innerHTML = '$'+Math.round(payment);

	}
	else
	{
		document.getElementById('estimatedPayment').innerHTML = '$'+0;
	}
}

function IsNumeric(sText)

{
   var ValidChars = "0123456789.";
   var IsNumber=true;
   var Char;

 
   for (i = 0; i < sText.length && IsNumber == true; i++) 
      { 
      Char = sText.charAt(i); 
      if (ValidChars.indexOf(Char) == -1) 
         {
         IsNumber = false;
         }
      }
   return IsNumber;
   
   }