formula at the top of the sheet to show the latest figure in column

Having problems with the following:

First Column Second Column Cumulative (B-A)
1 10 9
2 20 27
3 30 54
4 40 90

Every day,a new row is added and i want a formula at the top of the sheet to show the latest figure in column C.

Any ideas? thanks

Hi,

I've change your title for you and here's one way to do a sum at the top of column C

Assume your data starts in row2 down to row 100

=SUM(B2:B100)-SUM(A2:A100)