A flexible budget is a budget that adjusts or flexes for changes in the volume of activity. The flexible budget is more sophisticated and useful than a static budget, which remains at one amount regardless of the volume of activity.

Assume that a manufacturer determines that its cost of electricity and supplies for the factory are approximately $10 per machine hour (MH). It also knows that the factory supervision, depreciation, and other fixed costs are approximately $40,000 per month. Typically, the production equipment operates between 4,000 and 7,000 hours per month. Based on this information, the flexible budget for each month would be $40,000 + $10 per MH.

Now let's illustrate the flexible budget by using some data. If the production equipment is required to operate for 5,000 hours during January, the flexible budget for January will be $90,000 ($40,000 fixed + $10 x 5,000 MH). If the equipment is required to operate in February for 6,300 hours, then the flexible budget for February will be $103,000 ($40,000 fixed + $10 x 6,300 MH). If March requires only 4,100 machine hours, the flexible budget for March will be $81,000 ($40,000 fixed + $10 x 4,100 MH).

If the plant manager is required to use more machine hours, it is logical to increase the plant manager's budget for the additional cost of electricity and supplies. The manager's budget should also decrease when the need to operate the equipment is reduced. In short, the flexible budget provides a better opportunity for planning and controlling than does a static budget.