The estimated range highlights. Edit the range by left-clicking and dragging the cursor over all values in the row to sum, if desired. The selected rows are highlighted.

SUM is the spreadsheet equivalent of an open invite: it welcomes everything into the total, whether it belongs there or not.

If you don't have an existing file, use the blank worksheet in Excel. Type a zero in the first row of your column and drag your mouse down to the last row of the column to autofill it with zeros.