Assuming your headings are in row 1 and data start from row 2 and
down. To sum column C:C, one way:

=SUMPRODUCT(OFFSET(C1,COUNTA(C:C)-29,0,30,))

HTH
Kostis Vezerides

On Jul 3, 3:58 pm, Nick Krill
wrote:
How can I use sumproduct on the last 30 rows of a database whose number of
rows changes daily?