Checking For Empty Cells

I'm trying to see if the cells I'm about to populate are empty. Here's my code:

Counter = 0
Do While Counter < NoOfDays
        If Not (IsEmpty(ActiveCell.Offset(Counter, 0))) Then 
            MsgBox "Please Ensure Target Range Is Clear", vbCritical
            (exit statement)
         End If
         Counter = Counter + 1   
Loop

The active cell is J1 but this code doesn't detect cells already populated. Any ideas?