Economic Surplus

Economic surplus is the sum of the gains from trade in a market, comprising consumer surplus and producer surplus. It measures the benefit that participants derive from participating in a market, relative to their next-best alternatives.

Components

Consumer surplus is the difference between what consumers are willing to pay for a good and what they actually pay. It is measured by the area between the demand curve and the price line. Producer surplus is the difference between what producers receive and the minimum they would accept. It is measured by the area between the price line and the supply curve.

The sum of consumer surplus and producer surplus is total surplus, which measures the net benefit to society from the production and consumption of the good. In a competitive market, total surplus is maximised at the equilibrium.

Efficiency and Deadweight Loss

The concept of economic surplus provides the basis for the analysis of the efficiency of market outcomes. At the competitive equilibrium, total surplus is at its maximum, and any deviation from the equilibrium reduces total surplus.

A deviation reduces surplus in a way that can be measured. A tax, a subsidy, a price ceiling, or a price floor moves the quantity away from the equilibrium and creates a deadweight loss, which is the reduction in total surplus that is not offset by any gain to anyone. The deadweight loss is the triangle between the demand and supply curves over the range of the deviation.

Distribution

Economic surplus is also relevant to the analysis of distribution. The division of total surplus between consumers and producers depends on the elasticities of demand and of supply. When demand is inelastic relative to supply, consumers bear a larger share of a tax and receive a smaller share of a subsidy.

The distributional effects of policies are often as important as their effects on total surplus. A policy that raises total surplus may reduce the surplus of a particular group, and a policy that reduces total surplus may benefit a particular group. The assessment of policy must therefore consider both the total and the distribution.

Applications

The concept of economic surplus is used in cost-benefit analysis, where the change in surplus provides a measure of the welfare effect of a project or a policy. It is used in the analysis of international trade, where the gains from trade are measured by the increase in surplus. It is used in the analysis of regulation, where the effect of a regulation on surplus is compared with its benefits.

The measurement of surplus requires estimates of the demand and supply curves, which are difficult to obtain. The measurement is further complicated when markets are not competitive or when there are externalities, since the simple framework does not capture the relevant effects. The concept is therefore a guide to analysis rather than a precise measure.

Surplus and Market Intervention

The concept of economic surplus provides a framework for the analysis of market intervention. A price ceiling, set below the equilibrium, reduces the quantity supplied and creates a shortage. The loss of surplus is the deadweight loss, and the transfer from producers to consumers is the difference between the price and the ceiling.

A price floor, set above the equilibrium, reduces the quantity demanded and creates a surplus. The loss of surplus is the deadweight loss, and the transfer from consumers to producers is the difference between the floor and the price.

The analysis of these interventions illustrates the trade-off between the objectives that they serve and the efficiency costs that they impose. A price ceiling may make a good affordable, but it may also create shortages and reduce the quality of the good.

Taxation and Deadweight Loss

A tax drives a wedge between the price paid by consumers and the price received by producers, reducing the quantity traded and creating a deadweight loss. The size of the loss depends on the elasticities of demand and of supply: the more elastic the curves, the larger the reduction in quantity and the larger the loss.

The incidence of the tax, which is the division of the burden between consumers and producers, also depends on the elasticities. The less elastic side of the market bears the larger share of the burden, since it is less able to change its behaviour in response.

The analysis of the deadweight loss informs the design of tax policy. Taxes on goods with inelastic demand, such as necessities, raise revenue with smaller efficiency costs, but they may be regressive. Taxes on goods with elastic demand have smaller revenue and larger efficiency costs. The optimal design balances revenue, efficiency, and equity.

Surplus and International Trade

The concept of surplus is used in the analysis of international trade. When a country opens to trade, the price converges to the world price, and the change in surplus measures the gains from trade. For an importing country, consumers gain and producers lose, and the net effect is positive when the gains exceed the losses.

The analysis of trade policy uses the surplus framework. A tariff raises the domestic price, reduces imports, and creates a deadweight loss. It also transfers income from consumers to producers and generates revenue for the government. The net effect on welfare is typically negative for a small country.

The framework also shows the distributional effects of trade. The gains are concentrated among consumers, who are numerous and each of whom gains a small amount, while the losses are concentrated among producers, who are fewer and each of whom loses a large amount. This asymmetry helps to explain the political economy of trade policy.

Summary

Economic surplus is a versatile tool of welfare analysis, applied to the assessment of market interventions, of taxation, and of trade policy. Its use requires attention to the elasticities of demand and supply and to the distribution of the gains and losses.

See also

• Economic Efficiency
• Total Revenue
• Utility