A budget starts and ends within a specific period, or as we call it a Cycle. The duration of it will depend on your choice: Weekly, Monthly and Yearly.
The cycle filter will allow you to not only view your current performance in the budget but, also, your previous performances in previous budgets.
All you need to do is tap on the cycle drop-down in the budget details page, and a list will appear of the current cycle and previous cycles. Whenever a cycle finishes, it will be added to this list.