Yes, you can.

...
    ROUND(Sum(IIF(BETWEEN(Reservations.date, OldFrom, OldTo), 1, 0)*100/ ;
        Sum(IIF(BETWEEN(Reservations.date, ReportFrom, ReportTo), 1, 0), 2) AS percent, ; 
...

However, it would be simplier to use second select for that.

>Thx Sergey, you nailed it again.
>Do you think i can also retrieve in this same SELECT the percentage growth ( or reduction ) between CurRes and OldRes?
>
>
>>Try

SELECT ;
>>    Clients.ClientName, ;
>>    Sum(IIF(BETWEEN(Reservations.date, ReportFrom, ReportTo), 1, 0) as CurRes,;
>>    Sum(IIF(BETWEEN(Reservations.date, ReportFrom, ReportTo), Reservations.Amount, 0) as CurAmount, ;
>>    Sum(IIF(BETWEEN(Reservations.date, OldFrom, OldTo), 1, 0) as OldRes,;
>>    Sum(IIF(BETWEEN(Reservations.date, OldFrom, OldTo), Reservations.Amount, 0) as OldAmount, ;
>>  FROM Reservations JOIN Clients ;
>>        ON Reservations.ClientCode=Clients.Code  ;
>>  WHERE between( Reservations.date, ReportFrom, ReportTo ) ;
>>         OR between( Reservations.date, OldFrom, OldTo ) ;
>>  GROUP BY Clients.Code ;
>>INTO CURSOR crsResult	
>>