Why aren't selling and administrative costs not included in variable costing?

Selling and administrative costs are not included in variable costing because variable costing focuses solely on the direct costs associated with producing goods, such as direct materials and direct labor. These costs are variable in nature and fluctuate with production levels. In contrast, selling and administrative expenses are typically considered fixed costs, as they do not change directly with production volume and are incurred regardless of how much is produced. By excluding these costs, variable costing provides a clearer picture of the contribution margin related to production activities.