Disable Calender Date before current date using javascript

Make sure you add the following js and css files.

* jquery-1.4.1.min.js
* jquery.ui.core.js
* jquery.ui.datepicker.js
* jquery-ui-1.8.8.custom.css

Now paste the following code:

<script type="text/javascript">
    $(function () {
        var date = new Date();
        var currentMonth = date.getMonth(); // current month
        var currentDate = date.getDate(); // current date
        var currentYear = date.getFullYear(); //this year
        $("#<%= tbxRequestDeliveryDate.ClientID %>").datepicker({
            changeMonth: true, // this will allow users to chnage the month
            changeYear: true, // this will allow users to chnage the year
            minDate: new Date(currentYear, currentMonth, currentDate)
           
        });
    });
</script>

<asp:textbox id="tbxRequestDeliveryDate" runat="server" cssclass="text" xmlns:asp="#unknown">

For more detail click here