Future date not accept in asp.net

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

<script type="text/javascript">

function check_date()

{

var chkdate = document.getElementById("txtDate").value;

var edate = chkdate.split("/");

var spdate = new Date();

var sdd = spdate.getDate();

var smm = spdate.getMonth();

var syyyy = spdate.getFullYear();

var today = new Date(syyyy,smm,sdd).getTime();

var e_date = new Date(edate[2],edate[1]-1,edate[0]).getTime();

if(e_date > today)

 {

    alert("Date is not valid");

    return false;

 }

}

    </script>

onkeypress ="return check_date(event)" />