On the Request Wizard: Step 1, you can apply a level of granularity to the data request. Granularity specifies the level of time-based detail that is included in the report.
Valid values are Hour, Day, Week, Month, Quarter, Year, and Aggregated.
How Report Builder processes granularity
Suppose you choose a date range for a month with Month granularity. Requests show totals for the metric based on exactly one month's worth of data. If the date range of your request spans one quarter, the report shows three figures: one for each month unit, or fraction thereof. If today is March 18, choosing the last quarter returns one figure for January 1 - January 31, another figure for February 1 - February 28, and a final figure for March 1 - March 17.