function GetDateTimeForBiasSystemTime(GivenDateTime : TSystemTime; GivenYear : integer) : TDateTime;
var Year, Month, Day : word;
    Hour, Minute, Second, MilliSecond : word;
begin
  GivenDateTime.wYear := GivenYear;
  while not TryEncodeDayOfWeekInMonth(GivenDateTime.wYear, GivenDateTime.wMonth, GivenDateTime.wDay, GivenDateTime.wDayOfWeek, Result) do
    Dec(GivenDateTime.wDay);

  DecodeDateTime(Result, Year, Month, Day, Hour, Minute, Second, MilliSecond);
  Result := EncodeDateTime(Year, Month, Day, GivenDateTime.wHour, GivenDateTime.wMinute, GivenDateTime.wSecond, GivenDateTime.wMilliseconds);
end;

function GetBiasForDate(GivenDateTime : TDateTime) : integer;
var tzi : TIME_ZONE_INFORMATION;
begin
  GetTimeZoneInformation(tzi);
  if (GivenDateTime < GetDateTimeForBiasSystemTime(tzi.StandardDate, YearOf(GivenDateTime))) and
     (GivenDateTime >= GetDateTimeForBiasSystemTime(tzi.DaylightDate, YearOf(GivenDateTime))) then
    Result := (tzi.Bias + tzi.DaylightBias) * -1
  else
    Result := (tzi.Bias + tzi.StandardBias) * -1;
end;

function UTCToLocalDateTime(aUTC : TDateTime) : TDateTime;
begin
  Result := IncMinute(aUTC, GetBiasForDate(aUTC));
end;

function LocalDateTimeToUTC(aLocal : TDateTime) : TDateTime;
begin
  Result := IncMinute(aUTC, GetBiasForDate(aUTC) * -1);
end;

function LocalDateTimeToUTC(aLocal : TDateTime) : TDateTime;
begin
  Result := IncMinute(aLocal, GetBiasForDate(aLocal) * -1);
end;