Enter Values

units
Max quantity demanded when P = 0
units/$
Units decrease per $1 price increase
units
Qs = -c + dP. When c = 0, supply starts at origin
units/$
Units increase per $1 price increase
$
Price where quantity demanded = 0
units
Quantity demanded when price = 0
$
Price where quantity supplied = 0
units
Quantity supplied when P = choke price
Surplus Formulas
CS = ½ × Q* × (Pmax − P*)
PS = ½ × Q* × (P* − Pmin)
TS = CS + PS
P* = Equilibrium price | Q* = Equilibrium quantity | Pmax = Choke price | Pmin = Min supply price
Model Assumptions
  • Linear supply and demand curves
  • Perfectly competitive market (price takers)
  • No externalities, taxes, or price controls
  • CS = willingness to pay minus price paid
  • PS = price received minus variable cost (not profit)
For educational purposes. Not financial advice. Market conventions simplified.
Ryan O'Connell, CFA
Calculator by Ryan O'Connell, CFA

Supply & Demand Diagram

Equilibrium & Surplus

Equilibrium Price $24.00
Equilibrium Quantity 52.00
Consumer Surplus $676.00
Producer Surplus $450.67
Total Surplus $1,126.67

Detailed Breakdown

Choke Price $50.00
Min Supply Price $6.67
CS Share of TS 60.0%
PS Share of TS 40.0%

Surplus Interpretation

Concept Meaning Diagram Area
Consumer Surplus Willingness to pay minus price paid Blue triangle
Producer Surplus Price received minus variable cost Orange triangle
Total Surplus CS + PS (maximized at equilibrium) Both areas combined

Understanding Consumer & Producer Surplus

What Is Economic Surplus?

Economic surplus (also called total surplus or social surplus) measures the total benefit that buyers and sellers receive from market exchange. It is the sum of consumer surplus (benefit to buyers) and producer surplus (benefit to sellers). In a perfectly competitive market with no externalities, the free-market equilibrium maximizes total surplus.

Supply and demand diagram showing consumer surplus as the green area below the demand curve and above the equilibrium price, and producer surplus as the pink area above the supply curve and below the equilibrium price
At the equilibrium price (P1) and quantity (Q1), consumer surplus is the green area between the demand curve and the price, while producer surplus is the pink area between the price and the supply curve.
Surplus Equations (Linear Curves)
Demand: Qd = a - bP
Supply: Qs = -c + dP
Equilibrium: P* = (a + c) / (b + d)
CS = ½ × Q* × (Pmax - P*)
PS = ½ × Q* × (P* - Pmin)

Consumer Surplus vs. Producer Surplus

Consumer Surplus

Willingness to pay minus price paid
The blue triangular area above the equilibrium price and below the demand curve. Measures the net benefit to all buyers in the market.

Producer Surplus

Price received minus variable cost
The orange triangular area below the equilibrium price and above the supply curve. Note: PS is not the same as profit. Profit = PS minus fixed costs.

Market Efficiency & the First Welfare Theorem

The First Welfare Theorem states that under perfect competition, the equilibrium allocation maximizes total surplus. At the equilibrium price:

  • Every unit produced has a buyer willing to pay more than the cost of production
  • No additional trades could make both parties better off
  • Any deviation from equilibrium creates deadweight loss (a reduction in total surplus)
Scope Note: This calculator computes surplus under free-market equilibrium. For the effects of taxes on surplus and deadweight loss, use the Tax Incidence & Deadweight Loss Calculator.

Key Assumptions

  • Demand and supply curves are linear
  • All market participants are price takers (perfect competition)
  • No externalities, taxes, subsidies, or price controls
  • Complete information and zero transaction costs
  • Consumer surplus measures area under demand, above price
  • Producer surplus measures area above supply, below price

Frequently Asked Questions

Consumer surplus is the difference between what consumers are willing to pay for a good and what they actually pay. Graphically, it is the triangular area above the market price and below the demand curve. For linear demand Qd = a - bP, consumer surplus equals ½ × Q* × (Pmax - P*), where Pmax = a/b is the choke price (the highest price any consumer would pay).

Producer surplus is the difference between the price producers receive and the minimum price they would accept to supply the good. It equals revenue minus variable cost. Importantly, producer surplus is not the same as profit: profit equals producer surplus minus fixed costs. For linear supply Qs = -c + dP, producer surplus equals ½ × Q* × (P* - Pmin), where Pmin = c/d.

Total economic surplus is the sum of consumer surplus and producer surplus. It measures the total net benefit that buyers and sellers receive from participating in the market. The First Welfare Theorem states that competitive equilibrium maximizes total surplus — any deviation from equilibrium reduces total surplus, creating deadweight loss.

For linear curves, surpluses form triangles. First find equilibrium by setting Qd = Qs to get P* = (a + c) / (b + d) and Q* = (ad - bc) / (b + d). Then calculate: CS = ½ × Q* × (Pmax - P*) where Pmax = a/b, and PS = ½ × Q* × (P* - Pmin) where Pmin = c/d. Total surplus TS = CS + PS.

Competitive equilibrium maximizes total surplus (the sum of consumer and producer surplus). At equilibrium, every unit produced has a buyer willing to pay more than the production cost. Producing more or fewer units would reduce total surplus. This result assumes no externalities, perfect competition, and complete information.

When demand increases (shifts right), both equilibrium price and quantity rise, increasing both consumer and producer surplus. When supply increases (shifts right), equilibrium price falls and quantity rises, increasing consumer surplus while the effect on producer surplus depends on the elasticity of demand. The market always moves toward a new equilibrium that maximizes total surplus.
Disclaimer

This calculator is for educational purposes only and assumes linear supply and demand curves in a perfectly competitive market with no externalities. Real-world markets involve nonlinear curves, imperfect competition, externalities, and transaction costs. This tool should not be used for policy decisions.

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