function mortgage_payments(loan, i, term, interestonly)
{
	if (interestonly) 
		return interestonly_payments(loan, i);
	else
		return loan_payments(loan, i, term);
}

// calculate the monthly loan payment amount using the term as a year term (1 = 12 months)
// loan = the initial loan amount
// i = the annual interest rate
// term = the term of the loan
function loan_payments(loan, i, term)
{
	var i_monthly = i / 100 / 12;
	var t_monthly = term * 12;
	// loan(1 + interest)^360 x interest) / ((1 + interest)^360 - 1)
	return loan * Math.pow(1 + i_monthly, t_monthly) * i_monthly /
			   (Math.pow(1 + i_monthly, t_monthly) - 1);
}
// calculate the monthly loan payment amount using the term as a month term (1 = 1 month)
// loan = the initial loan amount
// i = the annual interest rate
// term = the term of the loan
function loan_payments_monthly(loan, i, term)
{
	var i_monthly = i / 100 / 12;
	var t_monthly = term;
	// loan(1 + interest)^360 x interest) / ((1 + interest)^360 - 1)
	return loan * Math.pow(1 + i_monthly, t_monthly) * i_monthly /
			   (Math.pow(1 + i_monthly, t_monthly) - 1);
}
// calculate teh monthly loan payment amount for an interest only loan
function interestonly_payments(loan, i)
{
	var i_annual = i / 100;
	return loan * i_annual / 12;
}
// calculate the principal reduction of the loan for the first 12 months
// loan = the initial loan amount
// i = the annual interest rate
// payment = the monthly payment amount
function principal_reduction(loan, apr, payment)
{
	var reduc = 0;
	var i_monthly = apr / 100 / 12;
	var arr = new Array();
	for (var i = 0; i < 12; i++)
	{
		var interest = loan * i_monthly;
		var principal = payment - interest;
		loan = loan - principal;
		reduc += principal;					
	}
	return reduc;
}


function calcPayments(formname)
{
	var loan = parseNumber(document.forms[formname].loanamt.value);
	var apr = parseNumber(document.forms[formname].apr.value);
	var impound = parseNumber(document.forms[formname].impound.value);
	var pmi = parseNumber(document.forms[formname].pmi.value);
	var term = parseNumber(document.forms[formname].term.value);
	var interestonly = getCheckedValue(document.forms[formname].interestonly) == "true";
	var payment = mortgage_payments(loan, apr, term, interestonly) + impound + pmi;
	payment = Math.round(payment*100) / 100;
	document.forms[formname].payment.value = payment; 
}