Demand curve & consumer surplus

Price / WTP
Quantity
Exact Consumer Surplus
Rectangle Approximation
Market Price
Controls & Calculations
Market Price (P)4.0
Rectangles (fineness)8
Hover a rectangle to see its Q-range, WTP from demand, and the market price.
Inverse Demand:
P = 12.0 − 1.0·Q
Each point on the demand curve is the maximum willingness to pay for that unit.
Quantity Demanded at P:
?
Exact Consumer Surplus:
?
Rectangle Approximation:
?
Exact CS = ½ × base × height. Approximation = Σ (WTP_group − P) × ΔQ.

Supply curve & producer surplus

Price / MC
Quantity
Exact Producer Surplus
Rectangle Approximation
Market Price
Controls & Calculations
Market Price (P)6.0
Rectangles (fineness)8
Hover a rectangle to see its Q-range, price received, and marginal cost (MC) from supply.
Inverse Supply:
P = 0.0 + 0.8·Q
We model a linear supply: P = c + d·Q. Adjust c and d below to explore.
Supply Intercept (c)0.0
Supply Slope (d)0.8
Higher d makes supply steeper; positive c shifts it up.
Quantity Supplied at P:
?
Exact Producer Surplus:
?
Rectangle Approximation:
?
Exact PS = ∫₀^{Qˢ} (P − MC(Q)) dQ. With linear supply, PS = Qˢ(P − c) − ½ d Qˢ².
Tooltips show: Consumer — Q-range, WTP, Price. Producer — Q-range, Price, MC. No WTA shown.
Slice
Q-range:
WTP:
Price: