A company has budgeted to produce 5,000 units of Product B per month. The opening and closing inventories of Product B for next month are budgeted to be 400 units and 900 units respectively. The budgeted selling price and variable production costs per unit for Product B are as follows:

$ per unit

Selling Price20.00

Direct costs6.00

Variable production overheard costs3.50

Total budgeted fixed production overheads are $29,500 per month.

The company absorbs fixed production overheads on the basis of the budgeted number of units produced. The budgeted profit for Product B for next month, using absorption costing, is $20,700. Explain, using appropriate calculations, why there is a difference between the profit figures for the month using marginal costing and using absorption costing.