About performing calculations in a query

You perform calculations in a query using:

Predefined calculations, called "totals," to compute the following amounts for groups of records or for all the records combined in the query: sum, average, count, minimum, maximum, standard deviation, or variance.
A custom calculation to perform numeric, date, and text calculations on each record using data from one or more fields. You need to create a new calculated field directly in the design grid for these types of calculations.

Instead of displaying a calculation's results, you can use them:

As criteria to determine the records the query selects or to determine which records to perform an action on.
To update data from an update query.