Query Designer - how to dynamically show previous month's results

Hi friends...new to the world of Query Designer and hoping to get some assistance from this wonderful community.  Scenario is this....looking to show in the same view a plan by month and then the change over the previous month.  Without hardcoding, how do I create this look?  Example would be as follows--

(Visible)               (Visible)          (Not Visible)          (Visible)

Cal Year/Mo          Plan          Prev Month Plan          Month Chg

Jan                         100             

Feb                         50                    100                    .5

Mar                         30                    50                      .6

Apr                         100                   30                     3.33

...

**Note: Regardless of what range of months the user enters, we would want to pull the previous month plan to complete the Month change calculation which is really just the month plan/prev month plan.

Thanks in advance for any and all insights!!