Though the flex budget is a good tool, it can be difficult to formulate and administer. One problem with its formulation is that many costs are not fully variable, instead having a fixed cost component that must be calculated and included in the budget formula. Also, a great deal of time can be spent developing cost formulas, which is more time than the typical budgeting staff has available in the midst of the budget process. Consequently, the flexible budget tends to include only a small number of variable cost formulas