Consumer Surplus Formula
Consumer surplus = ½ × Q × (Pmax - P).
Measure the economic benefit consumers gain when they pay less than their maximum willingness to pay.
The Formula
Consumer surplus measures the economic benefit received by buyers who would have been willing to pay more than the market price. It is the area of the triangle below the demand curve and above the market price line.
P_max is the maximum price any consumer would pay (the demand curve intercept), P_market is the actual market price, and Q is the quantity purchased at that price. The formula assumes a linear demand curve; for non-linear curves, consumer surplus is the integral under the demand curve above the price.
Consumer surplus represents real economic welfare. When a concert ticket costs $50 but you would have paid $120, your consumer surplus is $70. Total consumer surplus across all buyers in a market is a key measure of market efficiency and social welfare.
Price discrimination — charging different prices to different customers — captures consumer surplus for sellers. Airline dynamic pricing, student discounts, and subscription tiers are all attempts to extract more consumer surplus.
Deadweight loss occurs when markets are not at competitive equilibrium. Monopoly pricing or taxes reduce consumer surplus and total welfare. Welfare economics uses consumer and producer surplus to evaluate the effects of taxes, subsidies, price controls, and trade policies.
Variables
| Symbol | Meaning | Unit |
|---|---|---|
| CS | Consumer surplus | $ (currency) |
| Q | Quantity demanded at market price | units |
| P_max | Maximum willingness to pay (demand intercept) | $ |
| P_market | Actual market price | $ |
Example 1
Market price for a product is $30. The demand curve shows P_max = $70 at Q = 0, and Q = 200 at P = $30.
CS = ½ × 200 × (70 − 30) = ½ × 200 × 40
CS = $4,000 (total consumer surplus in this market)
Example 2
Price rises from $30 to $50, reducing quantity from 200 to 120. What is the new consumer surplus?
CS = ½ × 120 × (70 − 50) = ½ × 120 × 20
CS = $1,200 (a loss of $2,800 in consumer welfare from the price increase)
When to Use It
- Evaluating welfare effects of taxes, subsidies, and price controls
- Cost-benefit analysis of public projects and regulations
- Assessing monopoly welfare losses versus competitive markets
- Microeconomics coursework and policy analysis