Microeconomics
Supply and Demand
The fundamental model — how prices and quantities are determined in markets
Supply and demand is the foundational model of economics. Demand: how much consumers want at various prices (typically: lower price → more demanded). Supply: how much producers offer at various prices (typically: higher price → more supplied). They meet at equilibrium price and quantity. Shifts in either curve change equilibrium. Foundation of price theory, market analysis. Caveats: assumes competitive markets, rational agents, no externalities. Real markets often deviate. But: extremely useful framework. Adam Smith's "invisible hand" — markets coordinate through price.
- Demand curveHigher price → less quantity demanded (typically)
- Supply curveHigher price → more quantity supplied (typically)
- EquilibriumWhere supply and demand intersect
- Demand shiftIncome, preferences, related goods, expectations
- Supply shiftCosts, technology, suppliers, expectations
- FoundationAdam Smith, "Wealth of Nations" (1776)
Interactive visualization
Press play, or step through manually. The visualization is yours to drive — try it before reading on.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
Why supply-demand matters
- Pricing. Setting prices for products.
- Markets. Understanding how markets function.
- Public policy. Effects of taxes, subsidies, regulations.
- Business strategy. Production decisions.
- Economic forecasting. Predicting price movements.
- Education. Foundational economics.
- Daily life. Understanding market behavior.
Common misconceptions
- Always works. Many market failures.
- Demand = wanting. Specifically at given prices.
- Equilibrium permanent. Constantly shifting.
- Same in all markets. Different goods have different elasticity.
- Government always disrupts. Sometimes corrects market failures.
- Just two factors. Many factors shift curves.
Frequently asked questions
How does supply and demand work?
Markets bring buyers and sellers together. Demand: how much buyers want at each price. Supply: how much sellers offer at each price. Higher prices: more produced (supply up); less consumed (demand down). Lower prices: opposite. They meet at equilibrium — price where supply equals demand. Markets self-adjust toward equilibrium.
What shifts demand?
Several factors. (1) Income: more income → more demand for normal goods (less for inferior). (2) Tastes/preferences: changing demand. (3) Related goods: substitutes (rise in tea price → more coffee demand) and complements (rise in burger price → less bun demand). (4) Expectations: future price changes. (5) Number of buyers. (6) Demographics. Demand curve shifts left (less) or right (more).
What shifts supply?
Different factors. (1) Input costs (labor, materials): rising costs → less supply. (2) Technology: better tech → more supply. (3) Number of suppliers. (4) Expectations: anticipated price changes. (5) Government policies: taxes/subsidies. (6) Natural disasters, weather. Supply curve shifts left (less) or right (more).
What's market equilibrium?
Price where quantity supplied equals quantity demanded. Stable: if price above, surplus → price falls. If below, shortage → price rises. Self-correcting. Equilibrium price: market-clearing. Quantity at equilibrium: market quantity. Both: determined by supply and demand interaction.
What if supply and demand both shift?
Multiple cases. (1) Both increase: quantity definitely up; price ambiguous (depends on relative shifts). (2) Both decrease: quantity definitely down; price ambiguous. (3) Supply increases, demand decreases: price down; quantity ambiguous. (4) Supply decreases, demand increases: price up; quantity ambiguous. Predictions: quantity OR price ambiguous depending on shifts.
What's elasticity?
Responsiveness of quantity to price changes. Elastic demand: small price change → big quantity change (luxuries, substitutes available). Inelastic: small change → small change (necessities, addictive goods). Specific: price elasticity of demand = (% change in Q) / (% change in P). Elastic if >1; inelastic if <1. Affects: pricing strategies, tax incidence, policy effects.
What about market failures?
Times when markets don't reach efficient outcomes. (1) Externalities: costs/benefits not reflected in price (pollution). (2) Public goods: non-excludable, non-rival (national defense). (3) Information asymmetries: one party knows more (used cars). (4) Monopolies/oligopolies: single seller restricts supply. (5) Common-pool resources: tragedy of commons. Each: justifies government intervention.