Compare Validator for performing date validation

<asp:CompareValidator ID="CompareValidatorBookingDeadline" runat="server"

ControlToCompare="TextBoxTodayDate"

ControlToValidate="TextBoxExpiaryDate" Display="Dynamic"

ErrorMessage="Please check the date."

Operator="LessThanEqual"

Type="Date" 

ValueToCompare="<%= TextBoxSeminarDate.Text.ToShortString() %>">*</asp:CompareValidator>

The important thing is "ValueToCompare" property of the compare validator.