2.5 Consumer & Producer Surplus

What is consumer surplus (CS)

The difference between what a consumer is willing to pay for a good and what they actually pay (its market price).

How is consumer surplus shown on a diagram

The area above the price line and below the demand curve.

 - CS decreases as price increases as less people are prepared to pay the higher prices. (vice versa if the price decreases)

Show on a diagram the effect of a price decrease on consumer surplus.

What does the impact of a price change on consumer surplus depend on (2 + diagrams)

• also depends on whether the price increased or decreased

What is producer surplus (PS)

The difference between the price a producer receives and the (minimum) price they are willing to accept.

How is producer surplus shown on a diagram

The area below the price line and above the supply curve.

 - Anything the firm sells below p1 is because it is willing to sell to consumers at a discounted price
 - There is a price P below which the producer is unwilling to supply anything since the costs of production would not be covered

What does the impact of a price change on producer surplus depend on (2 + diagrams)

• also depends on whether the price increased or decreased

How to show on a diagram consumer and producer surplus together + what does their sum represent

Their sum represents the net benefit to society of this market's operations

Key concept link - efficiency

What are the four causes of changes in consumer & producer surplus

1. Price changes
    2. Shifts in demand
    3. Shifts in supply
    4. Government interventions (taxes & subsidies)

How does a price increase affect CS and PS

• CS falls (consumers pay more, buy less)
 • PS rises (producers receive higher price per unit)

How does a price decrease affect CS and PS

• CS rises (consumers pay less, buy more)
 • PS falls (producers receive less per unit)

How does an increase in demand affect CS and PS

• D shifts right → P ↑, Q ↑
 • CS rises (more consumers benefit from willingness to pay)
 • PS rises (producers sell more at higher price)

How does a decrease in demand affect CS and PS

• D shifts left → P ↓, Q ↓
 • CS falls (fewer consumers benefit)
 • PS falls (producers sell less at lower price)

How does an increase in supply affect CS and PS

• S shifts right → P ↓, Q ↑
 • CS rises (cheaper, more quantity for consumers)
 • PS may rise or fall depending on elasticity

How does a decrease in supply affect CS and PS

• S shifts left → P ↑, Q ↓
 • CS falls (consumers pay more, fewer bought)
 • PS rises (higher price per unit, fewer sold)

How does a tax affect CS and PS

• S shifts left → P consumers pay ↑, Q ↓
 • CS falls (pay more, buy less)
 • PS falls (receive less after tax)
 • Government collects tax revenue → part of surplus transferred

How does a subsidy affect CS and PS

• S shifts right → P consumers pay ↓, Q ↑
 • CS rises (pay less, buy more)
 • PS rises (receive more per unit, sell more)
 • Government pays subsidy cost

How does PED affect changes in consumer surplus

• Inelastic demand → Q falls slightly → CS ↓ slightly
 • Elastic demand → Q falls sharply → CS ↓ greatly

How does PES affect changes in producer surplus

• Inelastic supply → Q ↑ slightly → PS ↑ slightly
 • Elastic supply → Q ↑ significantly → PS ↑ significantly

What is total surplus

CS + PS → measures total welfare in the market.

How is market efficiency related to CS and PS

• Efficient market → total surplus maximised
 • Deadweight loss occurs when taxes, price floors, or ceilings reduce total surplus

Give an example of real-world application of CS and PS.

• Food market: price subsidies increase CS (cheaper food) and PS (farmers sell more)
 • Tax on cigarettes reduces CS (consumers pay more) and PS (producers sell less)

Why is understanding CS and PS important for government policy (3)

• Shows winners and losers of taxes/subsidies
 • Helps assess market efficiency and welfare effects
 • Guides policy design to maximise social welfare

✅ Key exam tips:

1. Always draw and label diagrams for CS and PS.
    2. Show shifts in demand or supply and highlight new CS/PS areas.
    3. Include elasticity effects on magnitude of changes.
    4. Link to market efficiency, welfare, and government policies.
    5. Use real-world examples: food, transport, tech products.