Lars

one way, assuming no header row:

=IF(ISERROR(OFFSET(A1,COUNTA(A:A)-12,)),"not enough
rows",SUM(OFFSET(A1,COUNTA(A:A)-12,):OFFSET(A1,COUNTA(A:A),)))

This also assumes the data is in column A

Regards

Trevor


"Lars" wrote in message
...
I have a spreadsheet with about 50 rows that gradually will be filled up
with
numbers. How can I make formula that will count and ad up only the 12 last
rows at any given time? The position of the last 12 rows will here
obviously
change over time, since more numbers will be added frequently.

Thanks very much for any help.


--
Lars
--
Lars