Add Header:
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit"
TagPrefix="asp" %>
Markup:
<asp:CalendarExtenderID="Calendar1"runat="server"
Enabled="True" TargetControlID="TextBox1"Format="dd/MM/yyyy" ></asp:CalendarExtender>
To disable a past date use the following code in the "Page load":
protected void Page_Load(object sender, EventArgs e)
{
Calendar1.StartDate = DateTime.Now;
}
To disable a future date use the following code in the "Page load":
protected void Page_Load(object sender, EventArgs e)
{
Calendar1.EndDate = DateTime.Now;
}