Consumer Surplus vs Producer Surplus: What's the Difference?

Consumer surplus is the benefit buyers gain when they pay less than they were willing to pay. Producer surplus is the benefit sellers gain when they receive more than the minimum price they were willing to accept. The difference is whose benefit is being measured: buyers’ or sellers’. In Cambridge International AS Level Economics, these are the meanings and significance of consumer surplus and producer surplus (9708, 2.5.1 and 2.5.2).

A simple example

Suppose a buyer would pay up to $10$ monetary units for an item, but its market price is $8$. The buyer’s consumer surplus on that item is $10-8=2$ monetary units.

Suppose the seller would accept a minimum of $5$ monetary units for the same item. The seller’s producer surplus is $8-5=3$ monetary units. Both can gain from the same exchange, but their surpluses need not be equal.

On a demand and supply diagram

The demand curve shows buyers’ willingness to pay for different quantities. Consumer surplus is the area below the demand curve and above the market price, up to the quantity traded.

The supply curve shows the minimum prices at which sellers are willing to supply different quantities. Producer surplus is the area above the supply curve and below the market price, up to the quantity traded. These areas combine the surplus from all the units exchanged, rather than just one item in the example.

A change in market price changes both areas. If price falls after supply increases, buyers gain consumer surplus, while the effect on producers depends on the new price and quantity. The size of each change depends partly on price elasticity: how responsive demand or supply is to a price change.

Common exam mistake: Do not call producer surplus profit. Producer surplus compares the price received with the minimum acceptable price represented by the supply curve; profit requires a separate comparison of revenue with costs.