Opportunity Cost

Every resource committed to one use is simultaneously withdrawn from all others. The economic cost of a decision therefore has two components: explicit costs, which are cash or accrual payments to outside parties, and implicit costs, which are the returns the decision-maker sacrifices by deploying resources already owned. Labour supplied by an owner, premises held rather than leased out, and equity capital tied up in the business all carry implicit costs even though no invoice is ever issued.

The measurement rule is comparative, not cumulative. You identify the feasible alternatives, rank them by value, and charge the decision with the highest-valued option that was actually surrendered. Alternatives ranked below the best one are irrelevant, because choosing the best forgone option would already have excluded them.

Accounting profit is revenue less explicit costs. Economic profit is revenue less the sum of explicit and implicit costs, so it equals accounting profit minus the total implicit cost of owner-supplied resources. That implicit charge is what economists call normal profit: the minimum return required to keep entrepreneurial effort and equity capital in their current use rather than moving them elsewhere.

A firm earning exactly normal profit shows positive accounting profit and zero economic profit. This is the equilibrium condition toward which perfectly competitive markets are pushed by entry and exit, and it explains why sustained positive economic profit is treated as evidence of barriers to entry, differentiated product, or a genuine cost advantage rather than ordinary business success.

The slope of a production possibility frontier is an opportunity cost: units of one good forgone per additional unit of the other. Its increasing steepness reflects rising opportunity cost as resources less suited to a task are redeployed. Comparative advantage is defined entirely in these terms, since a country specialises where its opportunity cost of production is lowest, not where its absolute productivity is highest.

In corporate finance the same logic sets the discount rate. The cost of equity is the return shareholders forgo on investments of comparable risk, which is why a project must clear that hurdle to add value. Incremental cash flow analysis extends this: land already owned enters a project appraisal at its market value or best alternative use, while sunk costs, having no alternative use remaining, are excluded.

Three operations recur. First, restate a reported accounting result as an economic result by subtracting forgone wages, forgone rent on owned assets, and a required return on invested equity. Second, distinguish costs that are genuinely avoidable and forward-looking from sunk expenditures and from allocated overheads that do not change with the decision. Third, read opportunity cost off a frontier or a two-country production table and convert it into a specialisation and trade conclusion.

The common error is arithmetical rather than conceptual: candidates identify the implicit items correctly and then add several alternatives together, or omit the equity charge because no cash left the firm. Charge one alternative, the best one, and charge it whether or not it was ever transacted.