Since most companies experience substantial variations from their expected activity levels over the period encompassed by a budget, the amounts in the budget are likely to diverge from actual results. This divergence is likely to increase over time. The only situations in which a fixed budget is likely to track close to actual results are when:
Costs are largely fixed, so that expenses do not change as revenues fluctuate
The industry is not subject to much change, so that revenues are reasonably predictable
The company is in a monopoly situation, where customers must accept its pricing