function DateQuarterEnd(const D: TDateTime): TDateTime;
var
  Year, Month, Day, Quarter: Word;
begin
  SysUtils.DecodeDate(D, Year, Month, Day);
  Quarter := 4 - ((12 - Month) div 3);
  // get 1st day of following quarter
  Month := 0;
  SysUtils.IncAMonth(Year, Month, Day, Quarter * 3 + 1);
  // required date is day before 1st day of following quarter
  Result := SysUtils.EncodeDate(Year, Month, 1) - 1.0;
end;
//delphi/2163