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ECONOMICS • MICROECONOMICS

Supply & Demand Market Equilibrium

Shift demand, supply and a per-unit tax to see equilibrium price, traded quantity, surplus and deadweight loss change.

● MARKET CLEARINGDemand ↔ supply
Quantity traded
Buyer price
Seller price
Deadweight loss

Reasoning inspector

live model state
Equilibrium quantity—
Buyer price—
Seller price—
Tax wedge—
Consumer surplus—
Producer surplus—
Tax revenue—
Deadweight loss—

Where supply meets demand

This model turns a textbook market diagram into an experiment. Change demand, supply or a tax and watch the equilibrium move while consumer surplus, producer surplus and deadweight loss respond.

LEARN WITH THE SIMULATION

Understand Supply & Demand Market Equilibrium by experimenting.

START HERE

Supply and demand analysis explains how a competitive market can coordinate buyers and sellers through a clearing price. This interactive model makes the equilibrium movable: demand strength, demand slope, the minimum supply price, supply responsiveness and a per-unit tax all change the price buyers pay, the price sellers receive, traded quantity and total surplus.

BUILD THE IDEA

What you should understand first

  • Solve for the intersection of linear demand and supply rather than reading equilibrium from a static graph.
  • Distinguish the price paid by buyers from the price received by sellers when a per-unit tax creates a wedge.
  • Connect lower traded quantity with changes in consumer surplus, producer surplus, tax revenue and deadweight loss.
  • Explain why the side of the market that is less responsive tends to bear more of a tax burden in richer elasticity models.

TRY IT YOURSELF

How does a per-unit tax change equilibrium and total surplus?

  1. Start with the default market and record equilibrium price and quantity when tax is zero.
  2. Increase the per-unit tax while keeping both curves fixed, then compare buyer and seller prices.
  3. Watch traded quantity, tax revenue and deadweight loss as the tax grows.
  4. Change the slopes and repeat to see how market responsiveness changes the size of the quantity response.
Read the visual:

The tax creates a wedge between the buyer and seller prices. Quantity traded falls relative to the no-tax equilibrium, some surplus becomes tax revenue, and some mutually beneficial trades disappear as deadweight loss.

WHY IT WORKS 01

Why the intersection moves

Equilibrium is not a fixed property of a product. It is the solution to two relationships at once: how much buyers want at each price and how much sellers are willing to provide. Changing an intercept shifts one side of the market, while changing a slope alters responsiveness. The intersection therefore changes because the underlying behavioral relationships changed.

WHY IT WORKS 02

Taxes change quantities as well as prices

A per-unit tax separates the buyer price from the seller price. Demand responds to the buyer price while supply responds to the seller price, so the model must solve both equations with the wedge included. The lost quantity is economically important because it represents exchanges that would have generated surplus in the undistorted market.

DO NOT MIX THESE UP

Common misconception

A tax does not simply add its full amount to the old market price while leaving quantity unchanged. In this model both prices and quantity adjust together. The graph is also a competitive partial-equilibrium model, not a claim that every real market has smooth linear curves or no market power.

PRACTICE CHALLENGE

Can you create a market where a tax changes quantity only a little, then one where it changes quantity much more?

  • Use the slope controls to make both sides of the market relatively unresponsive and apply a fixed tax.
  • Record the change in quantity and deadweight loss.
  • Make one or both curves more responsive, keep the same tax, and compare the new quantity loss.
Reveal the reasoning

Flatter or more quantity-responsive relationships produce a larger change in traded quantity for a given price wedge. Because deadweight loss comes from trades that disappear, a larger quantity response generally produces a larger efficiency loss in this linear partial-equilibrium model.

MODEL BOUNDARIES

What this simulation assumes

Every simulation simplifies reality or a mathematical system. These are the assumptions and limits to keep in mind while interpreting the results.

Model assumptions

  • Demand is linear and downward sloping while supply is linear and upward sloping over the displayed range.
  • The market is represented as a competitive partial equilibrium with a single homogeneous good and no strategic market power.
  • A per-unit tax creates a wedge between the buyer price and seller price, and tax revenue equals tax times traded quantity.

Model limitations

  • Real demand and supply curves can be nonlinear, shift for many omitted reasons, and may not represent a competitive market.
  • The welfare calculation omits externalities, administrative costs, distributional concerns, income effects and general-equilibrium feedback.

CONNECT IT

Where this matters

  • Introductory microeconomics and market equilibrium
  • Tax incidence and welfare analysis
  • Policy comparisons involving per-unit taxes
  • Understanding how curve shifts change prices and quantities

WORDS THAT MATTER

Key vocabulary

Market equilibrium
The price and quantity at which quantity demanded equals quantity supplied in the model.
Tax wedge
The difference between the price buyers pay and the price sellers receive when a per-unit tax is imposed.
Deadweight loss
The reduction in total surplus caused by trades that no longer occur after a distortion such as a tax.
Consumer surplus
The modeled difference between buyers' willingness to pay and the price they actually pay, aggregated over traded units.