In addition to grouping and sorting, you can add subtotals, grand totals, and other calculations to your reports. For example, you can calculate how much you spent on a given model of desk or office chair.
With your report still open in Layout view, start the Group, Sort, and Total
pane, click a grouping level, and then click More
Locate the “totaled” field and click the arrow next to it.
Use the Totals
dialog box to select the field you want to calculate, the type of calculation you want to use, such as a sum or average, and to set options such as subtotals and grand totals.
When you finish, your report displays the calculations.