The Joins Year over Year Report can be used to understand join cycles and trends on a year over year basis.
How to use it
Navigate to Reporting > Membership and click on the "Track Membership Growth" report
On the following page, you will see a graph showing joins on a monthly basis over a year.
You also have the options at the top left of the toolbar to add additional years for comparison, and the ability to filter by specific Member Types to compare trends at that level