Is your label too short to display the far right of the value?
Tweak your routine like so and then open your immediate/debug window (Ctrl+G) to see what was printed out
Code:
For i = 1 To 4
FirstPlacePercent(i) = (Stack(i) / StackSum) * 100
    Debug.Print i; Stack(i); StackSum, FirstPlacePercent(i)
Next i