Formula to sum in columns that change weekly

[Robert L. Salisbury]

I enter a column of data weekly into a spread sheet and then total each row
for the last 4,8& 12 weeks. As the column numbers to be added change weekly
I have to change the formula weekly. Is there a way to do this
automatically?

 

[J.E. McGimpsey]

Assuming no blanks, this will total the last 4, 8 and 12 weeks in
row 2:

=SUM(OFFSET($A$2,0,COUNTA($2:$2)-4,1,4)
=SUM(OFFSET($A$2,0,COUNTA($2:$2)-8,1,8)
=SUM(OFFSET($A$2,0,COUNTA($2:$2)-12,1,12)