JQuery Calculate Day Difference in 2 date textboxes

1) Html

<input type="text" id="firstDate" name="firstDate"/>
<input type="text" id="secondDate" name="secondDate"/>

2) Jquery

$("#firstDate").datepicker({

}); 
$("#secondDate").datepicker({
    onSelect: function () {
        myfunc();
    }
}); 

function myfunc(){
    var start= $("#firstDate").datepicker("getDate");
    var end= $("#secondDate").datepicker("getDate");
    days = (end- start) / (1000 * 60 * 60 * 24);
    alert(Math.round(days));
}

Jsfiddle working example here

This should do the trick

var start = $('#start_date').val();
var end = $('#end_date').val();

// end - start returns difference in milliseconds 
var diff = new Date(end - start);

// get days
var days = diff/1000/60/60/24;

Example

var start = new Date("2010-04-01"),
    end   = new Date(),
    diff  = new Date(end - start),
    days  = diff/1000/60/60/24;

days; //=> 8.525845775462964