cctime_calculate = function()
{
	var p = document.getElementById("cctime_balance").value;
	if ( p.length == 0 )
	{
		alert("Please enter your current credit card balance");
		return;
	}
	p = fixNumber(p);
	p = parseFloat(p);
	if ( isNaN(p) )
	{
	alert("Please enter the current balance as a number");
		return;
	}
	if ( p < 0 )
	{
		alert("Please enter a balance >= 0");
		return;
	}
	
	var rate = document.getElementById("cctime_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 greater than 0 and less than 35");
		return;
	}

	var spending = document.getElementById("cctime_spending").value;
	if ( spending.length > 0 )
	{
		spending = fixNumber(spending);
		spending = parseFloat(spending);
		if ( isNaN(spending) )
		{
			alert("Please enter the monthly spending as a number");
			return;
		}
	} 
	else spending = 0;
	
	if ( spending < 0 )
	{
		alert("Please enter a positive monthly spending");
		return;
	}

	var months = document.getElementById("cctime_months").value;
	if ( months.length == 0 )
	{
		alert("Please enter number of months");
		return;
	}
	months = fixNumber(months);
	months = parseFloat(months);
	if ( isNaN(months) )
	{
		alert("Please enter the number of months as  a number");
		return;
	}
	if ( months < 0 )
	{
		alert("Please enter a positive number of months");
		return;
	}
	
	// monthly rate:
	var m = rate / 1200;
	
	// calculate
	var nom = p * m ;
	var denom = 1 - Math.pow(1 + m, -1 * months);
	var x = spending + ( nom / denom );
	var interest = (months * x) - p - ( months * spending );

	var resel = document.getElementById("cctime_dt_results");

	var results = "<p>To pay off your credit card balance in " + months + " months, you will have to make a monthly payment of <b>" + formatDollars(x) + "</b>.</p>";

	results += "<p>You will pay a total of <b>" + formatDollars(interest) + "</b> in interest.</p>";
	
	resel.innerHTML = results;
	resel.style.display = "block";
}