A rolling budget adds a future accounting period's budget to replace a budget for an accounting period that has past. For example, a company's 2017 annual budget will become a rolling budget if in February 2017 it adds the budget for January 2018 to replace the January 2017 budget. At that point the rolling budget will cover February 1, 2017 through January 31, 2018. After February 2017 occurs, the rolling budget will consist of the 12 monthly budgets of March 1, 2017 through February 28, 2018.
The rolling budget is also referred to as a rolling horizon budget, a continuous budget, or a perpetual budget.