Fixed, Variable, Direct and Indirect Costs

Two different questions

Fixed versus variable asks how cost changes with activity. Direct versus indirect asks whether cost can be economically traced to a particular project, product or work package.

Fixed and variable behaviour

A fixed cost remains broadly stable within a relevant activity range and period. A variable cost changes with units, hours, transactions or another driver. Many real costs are mixed or step-fixed rather than perfectly fixed or variable.

Direct and indirect traceability

Direct labour, dedicated materials and a project-specific subcontract are usually traceable. Shared supervision, facilities, information systems or corporate services may require an allocation rule.

Why classification matters

• Scenario models need cost behaviour.
• Responsibility and change control need traceability.
• Pricing and full-cost analysis may require indirect allocation.
• Cash-flow planning needs timing as well as category.