HTML Markup:
First add Ajax control ToolkitScriptManager on page.
<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"> </asp:ToolkitScriptManager>
<asp:TextBox ID="txtfromdate" class="m-wrap span12" autocomplete="off" placeholder="" runat="server"></asp:TextBox>
<asp:CalendarExtender ID="CalendarExtender1" ClearTime="true" runat="server" TargetControlID="txtfromdate" Format="dd-MM-yyyy"> </asp:CalendarExtender>