When you are proposing a range to sum Excel firsts looks for a range of cells with numbers above the active cell then to the right?
If you use the Autosum, Excel will try to detect cells that are
above or right of it. If there are figures both immediately above
it and immediately right of it, then it will try to sum the ones
immediately above it. However, using the Autosum you can select a
block of cells and Excel will put totals at the end of them, again
opting for the bottom if columns of cells are involved, so you
could select a row of values or a column of values. You can also
just manually type in the cells you want to sum.