Calculate Mortgage Payment

I'm trying to create a mortgage payment calculator in Javascript and am having problems. My algorithm seems correct but it's not giving the right results. Im using this code:

function do_calc_payment(){var term = document.calc_payment.term.value;var rate = document.calc_payment.rate.value;var amount = document.calc_payment.amount.value;var j = rate / (12*100);var m = term * 12;var payment = amount * ( j / (1 - (1 + j) ^ -m))var result = "$"+Math.round((payment)*1000)/1000;if(isNaN(payment)){document.calc_payment.rate.value="";document.calc_payment.amount.value="";result="Not a Number";}if(payment.length>=15){result="Max Characters";}document.getElementById('new_payment').innerHTML = result;}