, Good afternoon.
Analyzing your situation, the result is very strange.
The formula is correct.
I suppose the cells Z3 and AA3 are formatted as DATE.
I also suppose that when entering the date you have typed as date and there being no possibility of entering as text.
Try doing the same procedure using other cells.
as the cell of the original date.
as the formula cell.
Format AC10 and AD10 as dates.
Enter the date.
Does the same problem happen ???
Do this and tell us the result.
We will be here and we will try to help you.
Belo Horizonte, Brasil