Profit depends on price relative to ATC

The same output rule can produce profit, break-even, or loss.

Always read ATC at the output selected by the marginal rule.

If P>ATC at the chosen quantity, the profit rectangle is (P-ATC)q. If P=ATC, economic profit is zero. If AVC≤ P<ATC, the firm operates at a loss because revenue covers variable cost and part of fixed cost. If P<AVC, it shuts down.

Read all cost curves at the P=MC output. A graph may show price above ATC at one quantity and below it at another. Only the chosen quantity measures profit. The rectangle’s height is the per-unit gap and width is firm output. If the gap is negative, report the absolute loss or retain the negative sign consistently.

Economic profit differs from producer surplus. At a competitive firm’s output, producer surplus is revenue minus variable cost, while profit is revenue minus total cost. Their difference is fixed cost. A firm can have positive producer surplus and negative profit when operation covers variable cost but not fixed cost.

Operate with a loss

Market price is $14. Rising MC equals $14 at 60 units. AVC is $10 and ATC is $16. The firm produces 60 because price covers AVC. Its loss is (16-14)60=$120, smaller than the fixed-cost loss from shutdown.

At that output, revenue is $840, variable cost is $600, and total cost is $960. Producer surplus is $240. Fixed cost is 960-600=$360. Profit is 240-360=-$120. The three totals confirm both operation and loss.

Zero economic profit does not mean zero producer surplus. At break-even, revenue covers variable and fixed opportunity costs, so producer surplus equals fixed cost while economic profit is zero. This is why the terms cannot be substituted.

In the long run, a price below minimum ATC leads to exit if conditions persist. The short-run table describes one firm before all inputs and firm count can adjust. Keep the horizon attached to the conclusion.

When price is below ATC, either report loss as the positive magnitude (ATC-P)q or report profit as the negative number (P-ATC)q. Mixing the two conventions creates sign errors. The shaded loss rectangle has height ATC-P and width firm output.

A break-even firm still has reason to produce. Zero economic profit covers normal return and every opportunity cost. It is not indifferent between production and shutdown unless price is also at the shutdown point. Minimum ATC and minimum AVC answer different boundaries.

If totals are supplied, profit is TR-TC. If price, ATC, and output are supplied, use the rectangle. The methods must agree. Multiplying price minus MC by output incorrectly treats the last unit’s cost as the average cost of every unit.

Producer surplus can remain positive during a loss because revenue exceeds variable cost. Subtracting fixed cost converts producer surplus into economic profit and explains why operation can be rational despite a negative result.

That distinction is especially useful in short-run shutdown questions.