This is probably a simple question, but I need help as I'm not very
proficient with spreadsheets.

In my spreadsheet, the last two rows are calculations. One shows the
difference between the last two row of data and the one immediately before it
(e.g., B26-B27), and the other shows the difference between the last row of
data and the first (B$1-B27). This works fine, except that I am constantly
adding new "last" rows of data. This means I have to keep updating the
calculation rows (e.g., changing B$3-B27 to B$1-B28 and B26-B27 to B27-B28).
I would like Excel to do this automatically as each new row is added, but I
don't know how.

Any help would be appreciated. Thanks.