function calculate()
{  
	var price = document.getElementById("purchaseprice").value;
	if ( price.length == 0 )
	{
		alert("Please enter the purchase price");
		return;
	}
	price = fixNumber(price);
	price = parseFloat(price);
	if ( isNaN(price) )
	{
		alert("Please enter the  purchase price as a number");
		return;
	}
	if ( price < 0 )
	{
		alert("Please enter a purchase price >= 0");
		return;
	}
	
	var rate = document.getElementById("rate").value;
	if ( rate.length == 0 )
	{
		alert("Please enter an interest rate");
		return;
	}
	rate = fixNumber(rate);
	rate = parseFloat(rate);
	if ( isNaN(rate) )
	{
		alert("Please enter the interest rate as a number");
		return;
	}
	if ( rate < 0 || rate >= 35 )
	{
		alert("Please enter a interest rate >= 0 and less than 35");
		return;
	}

	var months = document.getElementById("duration").value;
	if ( months.length == 0 )
	{
		alert("Please enter the # of months you loan will last");
		return;
	}
	months = fixNumber(months);
	months = parseFloat(months);
	if ( isNaN(months) )
	{
		alert("Please enter the # of months as a number");
		return;
	}
	if ( months <= 0 || months > 120 )
	{
		alert("Please enter a # of months between 1 and 120");
		return;
	}

	var downpayment = document.getElementById("down").value;
	if ( downpayment.length == 0 )
	{
		alert("Please enter a down payment");
		return;
	}
	downpayment = fixNumber(downpayment);
	downpayment = parseFloat(downpayment);
	if ( isNaN(downpayment) )
	{
		alert("Please enter the down payment as a number");
		return;
	}
	if ( downpayment < 0 )
	{
		alert("Please enter a down payment >= 0");
		return;
	}
	if ( downpayment >= price )
	{
		alert("Your down payment exceeds the car price, so you won't need a loan.");
		return;
	}
	
	var mrate = rate / 1200;

	var loanamount = price - downpayment;
	var payment;

	if ( rate == 0 )
	{
		payment = loanamount / months;
	}
	else
	{
		var factor = Math.pow(1 + mrate, months );
		payment = loanamount * ( mrate / (1 - 1/factor) );
	}
	
	var x = document.getElementById("results");

	var results = "<p>The amount of your loan will be <b>" + formatDollars(loanamount) + "</b>.";

	results += "<p>Your monthly payment will be <b>" + formatDollars(payment) + "</b>.";
	
	results += "<p>You will pay a total of <b>" + formatDollars(((payment * months) + downpayment) - price) + "</b> in interest.";
	
	x.innerHTML = results;
	x.style.display = "block";
}