Consumer Surplus Calculator
Calculate consumer surplus, producer surplus and total surplus from a linear demand curve, demand and supply equations, or a list of buyers.
Consumer surplus is the gap between what buyers would have been willing to pay and what they actually pay: the area under the demand curve and above the price. The calculator works from a straight-line demand curve, from demand and supply equations, or from a list of individual buyers' maximum prices.
How to use this tool
- Choose how you want to describe demand.
- Quick method: enter the choke price (where nobody buys), the market price and the quantity sold, plus the lowest supply price if you also want producer surplus.
- Equations: enter demand P = a − bQ and supply P = c + dQ, and the equilibrium is found for you.
- Buyer list: enter each buyer's willingness to pay and the price.
Formula
CS = ½ × Q × (P max − P)
PS = ½ × Q × (P − P min); equilibrium Q* = (a − c) ÷ (b + d)
P max is where demand meets the price axis, P min is where supply meets it, and P and Q are the market price and quantity. For a list of buyers, consumer surplus is the sum of (willingness to pay − price) over everyone whose willingness to pay is at least the price. Buyer lists require complete nonnegative numbers; displayed rows are capped at 400 while totals include all values. A positive quantity at the choke price is inconsistent with the quick linear-demand model.
Example
With demand P = 100 − 2Q and supply P = 10 + Q, the market clears where 100 − 2Q = 10 + Q, so Q* = 30 units and P* = $40. Consumer surplus is ½ × 30 × (100 − 40) = $900, producer surplus is ½ × 30 × (40 − 10) = $450, and total surplus is $1,350.
Frequently asked questions
What happens to consumer surplus when the price rises?
It shrinks for two reasons: buyers who stay pay more, and some buyers leave the market. With linear demand, the loss is the trapezoid between the old and the new price.
What is the choke price?
The price at which quantity demanded falls to zero, which is the vertical intercept of the demand curve. In P = a − bQ it is a.
Is consumer surplus the same as total willingness to pay?
No. Total willingness to pay is the whole area under the demand curve up to the quantity bought; consumer surplus is that area minus what buyers spent. The quick method shows both.
Can consumer surplus be negative?
Not for a voluntary purchase: a buyer whose willingness to pay is below the price simply does not buy, so their surplus is zero rather than negative.
Sources
Last updated: 2026-10-30