# Rolling and Moving Averages

In IBM® Cognos® Analytics - Reporting, to add a rolling or moving average, you must create summary and custom calculations using layout expressions Adding a row or column of calculated values.

The Rolling and Moving Averages interactive sample report includes rolling and moving calculations.

## Rolling Average

A rolling average continuously updates the average of a data set to include all the data in the set until that point. For example, the rolling average of return quantities at March 2012 would be calculated by adding the return quantities in January, February, and March, and then dividing that sum by three.

## Moving Average

A moving average calculates the average of a data set for a specified period. For example, the moving average of return quantities at March 2012 with a specified period of two would be calculated by adding the return quantities in February and March and then dividing that sum by two. In IBM Cognos Analytics - Reporting, you can use a prompt to specify the period.