How do absorption (full) costing and variable (contribution) costing differ, and how can absorption costing distort decisions?
A core FP&A interview question — asked in analyst and associate interviews across IB, PE, and the Big 4.
THE SHORT ANSWER
Under variable (marginal) costing, only variable production costs are in product cost; fixed manufacturing overhead is a period expense. Under absorption (full) costing — required for external IFRS/GAAP reporting — fixed manufacturing overhead is allocated into unit cost and therefore into inventory. The key distortion: because absorption costing capitalizes fixed overhead in inventory, profit moves with production volume, not just sales — building inventory (producing more than you sell) defers fixed cost into the balance sheet and inflates reported profit, while drawing inventory down depresses it. This can incentivize overproduction to 'make the numbers', and it makes full unit cost misleading for short-term decisions (special orders, make-vs-buy, dropping a product) where only incremental/variable costs and contribution are relevant — using full absorbed cost can wrongly reject profitable incremental business. So for external reporting you use absorption costing, but for internal decision-making and performance you use contribution/variable costing to avoid the volume-driven profit distortion and the trap of treating allocated fixed cost as relevant.
WHAT INTERVIEWERS LISTEN FOR
- ✓Variable costing: fixed mfg overhead is a period cost; absorption: it's in unit cost/inventory
- ✓Absorption makes profit move with production volume, not just sales
- ✓Overproduction inflates profit by deferring fixed cost into inventory
- ✓Use contribution/variable costing for short-term decisions; absorption for external reporting
COMMON MISTAKES
- ✗Not knowing absorption ties profit to production volume
- ✗Using full absorbed cost for incremental decisions
- ✗Thinking the two give the same profit when inventory changes
Reading isn't the same as answering under pressure.
Interviewers don't hand you the model answer — you deliver yours on a clock. Practice this and 1,000+ questions with AI feedback on every answer.
RELATED QUESTIONS
- How do you build a pricing model?
- How do you present a scenario analysis to the board?
- How would you evaluate entering a new market?
- Walk me through using sensitivity analysis to inform a strategic decision.
- A company is considering investing in a new project with a projected 5-year payback period. What are the key factors to consider when evaluating the project's viability, and how would you present your findings to stakeholders?
- What are some common challenges that arise when implementing a driver-based planning approach in a company with a complex organizational structure and multiple stakeholders? How would you address these challenges and ensure a successful implementation?