Consumer Surplus Calculator — Demand Curve Welfare
Consumer surplus measures the benefit buyers receive when they pay less than their maximum willingness to pay. Enter the demand intercept (Pmax), market price, and quantity to compute the surplus triangle and total consumer value.
CS = ½ × (Pmax − P) × Q — the welfare gain to buyers
Demand intercept (Pmax): 100 | Price gap (Pmax − P): 40
- 1
Price gap (Pmax − P)
100 − 60 = 40The height of the consumer surplus triangle on the demand curve. - 2
Consumer Surplus
½ × 40 × 80 = 1,600
How does this calculator work?
Consumer surplus = ½ × (Pmax − P) × Q, the triangle between the demand curve and the price line. Enter the maximum willingness to pay (demand intercept), market price, and quantity to see total surplus, total consumer value, and the demand-curve plot.
Formula
How this is calculated
Consumer surplus is the area of the triangle that lies between the demand curve and the market price line, to the left of the equilibrium quantity. For a linear demand curve P = Pmax − slope × Q, this area is exactly a right triangle with base Q and height (Pmax − P), giving CS = ½ × (Pmax − P) × Q.
The demand intercept Pmax is the highest price that any consumer in the market would willingly pay — often estimated from survey data, experiments, or a calibrated demand model. The market price P is the prevailing price actually charged. The quantity Q is how many units are sold at that price. When the price falls, Q typically rises and the surplus triangle grows — reflecting the additional welfare that lower prices create for buyers.
Total consumer value is the sum of consumer surplus and total spending (P × Q); it represents the aggregate amount buyers would have been willing to pay if each unit were priced exactly at their personal willingness to pay. The surplus percentage shows what fraction of total consumer value is captured as surplus rather than paid as revenue to sellers. This calculator assumes a linear (straight-line) demand curve; real demand curves can be curved, in which case the true CS may differ.
Frequently asked questions
Consumer surplus is the "bargain" buyers receive — the difference between what they would have been willing to pay and what they actually paid, summed across all buyers. A consumer willing to pay £100 for a product priced at £60 gains £40 of surplus.
A lower market price increases consumer surplus in two ways: each existing buyer gains more (the height of the surplus triangle grows) and more buyers are attracted into the market (the base of the triangle grows). The relationship is non-linear — halving the price typically more than doubles the surplus.
Deadweight loss is the surplus that is destroyed when a market is inefficient — for example when a tax or a monopoly raises the price above the competitive equilibrium. The calculator measures surplus at the given price; to find deadweight loss, compare this to the surplus at the competitive price.
Also known as
TG we-Calculate Editorial Team. (2026). Consumer Surplus Calculator — Demand Curve Welfare [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/consumer-surplus-calculator
TG we-Calculate Editorial Team. "Consumer Surplus Calculator — Demand Curve Welfare." TG we-Calculate. 2026. https://we-calculate.com/calculator/consumer-surplus-calculator.
TG we-Calculate Editorial Team, "Consumer Surplus Calculator — Demand Curve Welfare," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/consumer-surplus-calculator
@misc{wecalculate_consumer_surplus_calculator, title = {Consumer Surplus Calculator — Demand Curve Welfare}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/consumer-surplus-calculator}}, year = {2026}, note = {TG we-Calculate} }
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