#pas
procedure IncMonths( var SystemTime : TSystemTime; MonthsNum : Integer );
{* Increases/decreases month number in TSystemTime record onto given
   months count (can be negative). Correct result is not garantee if
   day number is incorrect for newly obtained month. }
.............
//[procedure IncMonths]
procedure IncMonths( var SystemTime : TSystemTime; MonthsNum : Integer );
var M : Integer;
    DateTime : TDateTime;
begin
   M := SystemTime.wMonth + MonthsNum - 1;
   Inc( SystemTime.wYear, M div 12 );
   SystemTime.wMonth := M mod 12 + 1;

   // Normalize wDayOfWeek field:
   SystemTime2DateTime( SystemTime, DateTime );
   DateTime2SystemTime( DateTime, SystemTime );
end;