A rolling forecast adds a new period each time one closes. A twelve-month rolling forecast prepared in March, for example, runs through the following February. This keeps the planning horizon constant and avoids the common problem of a budget that says nothing useful about the months right after year-end.
Rolling forecasts reflect current expectations, which change as evidence arrives. They work best alongside a fixed budget, not instead of one. The budget records the target management adopted, and the forecast shows where the business now expects to land. Keeping the two separate makes variance analysis meaningful.