calculate loan cost

$.getAnnuiPayment = function(amount, months, rate) {
        /* Calculates the monthly payment from annual percentage
     rate, term of loan in months and loan amount. **/
        var interest = 0.0;
        var principal = 0.0;
        var acc = 0;
        var base = 1 + rate / 1200;

        for (var i = 1; i <= months; i++) {
            acc += Math.pow(base, -i);
        }

        var payment = (amount / acc);

        interest = amount * rate / 1200;
        principal = payment - interest;

        return {
            pay: payment,
            fee: $.termfee,
            principal: principal,
            interest: interest
        };
    };