dt_mtgpay_calculate = function()
{
	var price, down, rate, years;
	try
	{
		price = DT_F.getFormFloat( "dt_mtgpay_price", "Please enter the purchase price", "Please enter the purchase price as a number" );
		if ( price < 0 ) {
			throw("Please enter a purchase price >= 0");
		}
		down = DT_F.getFormFloat( "dt_mtgpay_down", "Please enter a down payment", "Please enter the down payment as a number" );	
		if ( down < 0 ) {
			throw("Please enter a down payment >= 0");
		}
		if ( down > price ) {
			throw("Your down payment is greater than your purchase price.  Therefore, you don't need a loan.");
		}
		rate = DT_F.getFormFloat( "dt_mtgpay_rate", "Please enter an interest rate", "Please enter the interest rate as a number" );
		if ( rate <= 0 || rate >= 20 ) {
			throw("Please enter an interest rate greater than 0 and less than 20");
		}
		years = parseInt( document.getElementById("dt_mtgpay_years").value );
	}
	catch ( err )
	{
		alert(err);
		return;
	}

	var loanAmount = price - down;
	var payment = DT_F.calcPayment(loanAmount, rate, years);

	var x = document.getElementById("dt_mtgpay_results");

	var results = "The amount of your loan will be <b>" + DT_F.formatDollars(loanAmount) + "</b>.";
	results += "<br><br>Your monthly payment will be <b>" + DT_F.formatDollars(payment) + "</b>.";
	
	if ( years == -1 ) {
		results += "<br><br><i>With an interest only mortgage, you will never own your house outright.</i>";
	}

	x.innerHTML = results;
	x.style.display = "block";
};