The code doesn't calculate or show any Results

I'm a noob of HTML5 & Jquery. I've built a piece of code to calculate Loan Amount based on Term & Interest. But it seems doesn't work on my own. The numbers aren't calculated automatically and stay at 0. I appreciate any helps. Thank you everyone.

This is the Script for pasting on Wordpress Site

<script>
        function pmt(rate_per_period, number_of_payments, present_value, future_value, type){
                if(rate_per_period != 0.0){
                    // Interest rate exists
                    var q = Math.pow(1 + rate_per_period, number_of_payments);
                    return -(rate_per_period * (future_value + (q * present_value))) / ((-1 + q) * (1 + rate_per_period * (type)));

                } else if(number_of_payments != 0.0){
                    // No interest rate, but number of payments exists
                    return -(future_value + present_value) / number_of_payments;
                }
                return 0;
            }


        function calcLoanezi(){

            var interest;
            if ($( "#invoice" ).val() =< 5000) {interest = 0.12}
            else if ($( "#invoice" ).val() >= 5001 && $( "#invoice" ).val() <= 10000) {interest = 0.10}
            else if ($( "#invoice" ).val() >= 10001 && $( "#invoice" ).val() <= 20000) {interest = 0.08}
            else if ($( "#invoice" ).val() >= 20001 && $( "#invoice" ).val() <= 35000) {interest = 0.0725}
            else if ($( "#invoice" ).val() >= 35001 && $( "#invoice" ).val() <= 60000) {interest = 0.0695}              
            else if ($( "#invoice" ).val() >= 60001 && $( "#invoice" ).val() <= 100000) {interest = 0.0675}

            var months;             // Lifetime of loan (in years)
            if ($("#term").val() >=60) {interest = interest+0.01}                   
            present     = $( "#invoice" ).val(),        // Present value  of loan
            future      = 0,        // Future value of loan
            beginning   = 0;        // Calculated at start of each period
            brokerage   = present * 0.06;

            var payment = -pmt((interest / 12), months, (Number(brokerage) + Number(present)), future, beginning);

            var payment_2dp_exgst = payment.toFixed(2);
            var payment_2dp_gst = ((payment*1.1)-payment).toFixed(2);
            var payment_2dp_incgst = (Number(payment_2dp_exgst) + Number(payment_2dp_gst)).toFixed(2);


            $( "#monthlyex" ).val("$"+payment_2dp_exgst);
            $( "#monthlygst" ).val("$"+payment_2dp_gst);
            $( "#monthlyinc" ).val("$"+payment_2dp_incgst);

        }

        $( document ).ready(function() {
        $( "#invoice" ).keyup(function(){
            calcLoanezi();
        });
        $("#term").on('change', function() {
            calcLoanezi();
        });
        });

    </script>

It doesn't show any results