An alternative approach to incremental budgeting is zero-based budgeting. This means that each expenditure budget starts with a zero allocation each year. Managers must justify each element of the budget they propose. This has the advantage of making managers think proactively about what funds they need. It also avoids the tendency simply to add a percentage of the previous year’s budget or assume that expenditure will remain the same. However, one major disadvantage of this approach is the increased demand on staff time, which is an expensive resource with an opportunity cost.