... total figure goes in g3, the week
cells read left to right, so it would be in b3,c3,d3,e3,f,3,, but in
g3 i need answer of diff everytime i put in a new week...ie
c3-b3...d3-c3 don't care about b3 anymore...

If I understand the problem statement now, maybe putting this in g3 would
help. (Combine all 3 lines into one formula.)

=IF(COUNT(B3:F3)1,
OFFSET(A3,0,COUNT(B3:F3),1,1)-
OFFSET(A3,0,COUNT(B3:F3)-1,1,1),"")