Producer surplus

Sellers, like buyers, often come away with more than the bare minimum they would have accepted. That extra is producer surplus.

Producer surplus is the difference between the price a seller receives and the lowest price they would have been willing to accept. It is the gain producers capture from selling at the market price rather than at their own cost floor, and the mirror image of consumer surplus.

Where it comes from

Just as buyers vary in willingness to pay, sellers vary in their costs. At a single market price, every seller whose cost is below that price earns a margin, and only the highest-cost seller still in the market, the marginal producer, earns nothing extra. Summed across all sellers, those margins are producer surplus: the reward for being able to supply at less than the price the market sets.

Surplus and welfare

Producer surplus and consumer surplus together measure the total welfare a market generates, the gains from trade shared between the two sides. Anything that blocks mutually beneficial trades, a tax, a price control, a monopoly restricting output, shrinks the combined surplus and creates deadweight loss. Policy debates about markets are, at bottom, often arguments about how big the total surplus is and how it is divided between buyers and sellers.

Not the same as profit

Producer surplus is related to profit but not identical to it, because surplus is measured against the cost of supplying each unit, while profit also nets out fixed costs. In the short run a firm can earn producer surplus yet still make a loss after fixed costs, which is why a firm may rationally keep producing at a price that does not cover everything, so long as it covers the cost of producing each unit.

Producer surplus completes the picture of who gains from a market and by how much. With consumer surplus, it lets economists ask not just whether trade happens but how much value it creates, and what is lost when something gets in its way.