It’s probable that one of the most frequent calculations you’ll make in Excel is to sum, or add up, a series of numbers. Luckily, summing is also one of the easiest calculations to make, with the AutoSum feature just a click away.
Click in a cell below or at the right of the series of cells you want to sum.
Make sure the selection rectangle encloses all the cells you want to sum. If you’ve accidentally included any unwanted cells or omitted any desired cells, move the mouse pointer over a corner of the selection until a two-headed arrow appears, and then drag the selection rectangle to resize it so that it includes all the cells you want. You can also move the entire selection rectangle by pointing to a side of the rectangle and dragging it to a new location.