For certain budgets, you might want to "rollover" your available balances
from one period to the next. For example, you might want to spend more on
eating out this month if you did not eat out enough last month.
Let's say you have a budgeted $100 for a tag this month but spent only $75.
Then $25 rolls over and your available amount for the next month would be increased by $25.
Similarly, if you spend $120, then the next month leaves you with $20 less available.
Rollover amounts are reset at the start of every year. Any positive or negative balances will be rolled over from one period to the next thereafter.