Surplus vs. Shortage: What's the Difference?

The Definitions

A surplus, also called excess supply, occurs when the price is above the equilibrium price, so quantity supplied exceeds quantity demanded. Goods sit unsold. A shortage, also called excess demand, occurs when the price is below the equilibrium price, so quantity demanded exceeds quantity supplied and some willing buyers cannot get the good. Both are measured as a horizontal distance on the diagram: at the given price, the gap between the point on the supply curve and the point on the demand curve. Neither term describes the total amount of a good in existence — both are statements about a specific price.

Reading Them Off the Graph

Draw a horizontal line at the stated price. If that line sits above the intersection, the supply curve is to the right of the demand curve at that height, and the horizontal gap is the surplus. If the line sits below the intersection, the demand curve is to the right, and the gap is the shortage. A useful memory aid: a price ceiling must be below equilibrium to have any effect, and ceilings create shortages; a price floor must be above equilibrium to bind, and floors create surpluses. A ceiling set above the equilibrium price or a floor set below it is simply non-binding and changes nothing.

Real-World Examples

Rent control is the standard shortage example: a legal maximum rent below the market-clearing level means more households want apartments than landlords offer, producing waiting lists, informal side payments, and, over the long run, weaker incentives to build or maintain units. The minimum wage is the standard surplus example within the basic competitive model: a wage floor above the market-clearing wage means more people want to work at that wage than employers wish to hire, and the surplus of labor is unemployment. Economists actively debate the size of that effect empirically, particularly where employers have wage-setting power, but the diagram itself is the required starting point on an exam.

What They Have in Common

Both are disequilibrium states, and in an unregulated market both are temporary — price movement eliminates them. Both also destroy value relative to the equilibrium outcome, because in each case some trades that both a buyer and a seller would have willingly made do not occur; that forgone value is deadweight loss. And in both cases, when price is prevented from adjusting, some other allocation mechanism takes over: queues and connections under a shortage, non-price competition and government purchases of the excess under a surplus. The difference between them is entirely a matter of which side of the equilibrium price the market is stuck on.