There is no need to write any custom code if your are trying to validate your textboxes date values which are in UK format. You can use CompareValidator to perform this action. Download the attached project to see the solution in action. Make sure you have set up the page to use the desired culture with <%@ Page culture="your culture" %>. Default.aspx ------------------ <%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" Culture="en-GB" %> <!DOCTYPE ......