Plain definition
Variable costs change in total as output, sales, or another activity driver changes. Materials, sales commission, or delivery charges may vary with units, but the unit rate is stable only within stated purchasing and operating conditions.
Illustrative example
Monetary examples use Saudi riyals (SAR). The same principles apply in other currencies.
A manufacturer uses material per unit. A 2,000-unit order appears to add variable cost, but the supplier requires an expedited shipment worth . The estimator includes both the unit cost and the order-specific delivery cost before accepting the price.
Why it matters
A variable cost is not necessarily proportional forever. Volume discounts, overtime, waste, and freight thresholds can change the relationship.
Practical consequence
Identify the real driver, test the unit rate against recent invoices, and include order-specific changes in the decision rather than applying a historic average blindly.
Try your own numbers
See the unit volume needed to cover fixed costs, and the planned profit at a chosen volume.
Break-even