javascript - addition

Hi, I am new to this site and javascript.

I am trying to get the below function to work, however total_rate returns NaN instead of a number. I am not sure what I did wrong any help would be appreciated. Thanks.

if (document.frm_emplyee_data.cbo_PayCycle.value == "M1" || document.frm_emplyee_data.cbo_PayCycle.value == "W2")

{
var num_pay_rate = parseFloat(document.frm_emplyee_data.txt_payrate.value);
var num_acct_rate1 = parseFloat(document.frm_emplyee_data.txt_acct_dist_rate1.value);
var num_acct_rate2 = parseFloat(document.frm_emplyee_data.txt_acct_dist_rate2.value);
var num_acct_rate3 = parseFloat(document.frm_emplyee_data.txt_acct_dist_rate3.value);

var total_rate = (num_acct_rate1 + num_acct_rate2 + num_acct_rate3);

if (total_rate != num_pay_rate)
{
alert("Pay Rate must be equal to sum of all rate fields in Account Distribution" + total_rate );
document.frm_emplyee_data.txt_payrate.focus();
flag=0;
return false
}
}