<asp:regularexpressionvalidator id="regxtxtfromdt"
runat="server"
errormessage="*"
forecolor="Red" controltovalidate="txtfromdt" setfocusonerror="true" validationexpression="^(((0[1-9]|[12]\d|3[01])\/(0[13578]|1[02])\/((19|[2-9]\d)\d{2}))|((0[1-9]|[12]\d|30)\/(0[13456789]|1[012])\/((19|[2-9]\d)\d{2}))|((0[1-9]|1\d|2[0-8])\/02\/((19|[2-9]\d)\d{2}))|(29\/02\/((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$"
validationgroup="vgsub"></asp:regularexpressionvalidator>
It includes all leap and non leap years