Revise Consumer and producer surplus for Cambridge 9708 (2.5)

Consumer surplus is the economic measure of a consumer's benefit from a market transaction. It is calculated as the difference between the highest price a consumer is willing to pay for a good or service and the actual price they do pay (the market price). For example, if you are willing to pay £5 for a coffee but only pay £3, your consumer surplus is £2. On a demand and supply diagram, the total consumer surplus for the entire market is represented by the area below the demand curve and above the equilibrium price line, extending to the quantity traded. This area signifies the collective 'extra' value or utility that consumers receive over and above what they paid for the product.

Producer surplus is the counterpart to consumer surplus, measuring the benefit to producers. It is defined as the difference between the price producers actually receive for a good and the minimum price they would have been willing to accept. This minimum acceptable price is determined by their marginal cost of production, as represented by the supply curve. If a firm receives £10 for a product that cost them £6 to produce, their producer surplus is £4. In a diagram, total producer surplus is the area above the supply curve and below the equilibrium price line, up to the quantity sold. It is a measure of the collective profit and economic rent producers gain from participating in the market.

Economic welfare, also known as community or total surplus, is the sum of consumer surplus and producer surplus. It represents the total net benefit to society from the production and consumption of a good. In a free market, the equilibrium price and quantity are where the demand and supply curves intersect. At this point, economic welfare is maximised. This outcome is described as being allocatively efficient because resources are allocated in a way that maximises societal wellbeing. Any deviation from this equilibrium, whether through overproduction or underproduction, will result in a lower total surplus and a state of allocative inefficiency, creating a 'deadweight loss' to society.

Government-imposed price controls, such as price ceilings (maximum prices) and price floors (minimum prices), disrupt the market equilibrium and have significant welfare effects. A price ceiling set below equilibrium causes a shortage. While some consumers benefit from the lower price, the overall consumer surplus may fall due to the reduced quantity available. Producer surplus unambiguously decreases. Conversely, a price floor set above equilibrium causes a surplus (excess supply). Producers who can sell at the higher price benefit, but overall producer surplus may fall due to the lower quantity sold. Consumer surplus always decreases. In both cases, the total economic welfare is reduced, creating a deadweight loss which represents the value of trades that no longer happen.

An indirect tax (e.g., VAT) levied on producers shifts the supply curve vertically upwards by the amount of the tax. This leads to a new, higher market price for consumers (Pc) and a lower price received by producers (Pp), with the quantity traded falling. Consequently, both consumer surplus and producer surplus shrink. The government gains tax revenue, represented by the rectangular area between Pc and Pp. However, the reduction in consumer and producer surplus is greater than the government's tax revenue. This net loss in total welfare is the deadweight loss of the tax, representing the efficiency loss from transactions that are no longer beneficial for buyers or sellers at the new post-tax prices.