Supply, Demand & Elasticity

Price is not something a manager simply chooses — it emerges from the tug-of-war between what buyers will pay and what sellers will offer. This lesson covers that tug-of-war (supply and demand) and then zooms in on the single most useful concept in all of pricing: elasticity — how sharply quantity responds to a change in price. Master elasticity and you can answer the question that haunts every pricing meeting: "If we raise the price, what happens?"

Part 1 — Supply, demand, and the price that clears the market

Two forces meet in every market:

• The demand curve slopes downward: as price rises, buyers want less (and vice versa). This is the "law of demand."
• The supply curve slopes upward: as price rises, sellers will offer more.

Where they cross is the equilibrium price — the one price at which the quantity buyers want exactly equals the quantity sellers offer. Above it, surplus (unsold goods) pushes price down; below it, shortage pushes price up. Markets constantly grope toward this clearing price.

What matters for managers is what shifts these curves:

• Demand shifts with income, tastes/trends, the price of substitutes and complements, expectations, and the number of buyers. (A fitness craze shifts demand for gym apps right — more demanded at every price.)
• Supply shifts with input costs, technology, the number of sellers, and regulation. (Cheaper cloud computing shifts the supply of software services right.)

The manager's read: when you see a price moving in your market, ask which curve shifted and why. A price spike from surging demand (act fast, expand) means something very different from one caused by a supply shock (a competitor's factory fire — temporary). Same symptom, opposite responses.

Part 2 — Elasticity: how much does quantity respond?

Knowing demand slopes down isn't enough; you need to know how steeply. Price elasticity of demand measures the sensitivity:

Price Elasticity of Demand = % change in Quantity ÷ % change in Price

It's negative (price up, quantity down), so we usually talk about its absolute value:

• |E| > 1 → Elastic: quantity is very responsive (a small price rise sheds lots of buyers).
• |E| < 1 → Inelastic: quantity is not very responsive (you can raise price and lose few buyers).
• |E| = 1 → Unit elastic: quantity moves exactly in proportion.

What makes demand elastic or inelastic? Four big drivers:

1. Substitutes. Many close alternatives → elastic (one brand of bottled water). Few → inelastic (a patented drug).
2. Necessity vs. luxury. Necessities are inelastic (insulin, gasoline); luxuries elastic (cruises, fine dining).
3. Share of budget. Cheap items are inelastic (salt, a phone app); big-ticket items elastic (cars).
4. Time horizon. Demand is more elastic over the long run — people need time to find alternatives (gas demand barely moves this week, but high prices eventually push people to fuel-efficient cars).

This single concept explains a thousand business facts: why luxury brands can hike prices (inelastic, loyal buyers), why airlines fare-match instantly (elastic, easy comparison), and why utilities are regulated (inelastic necessity = pricing power that must be checked).

Part 3 — Why elasticity rules pricing: the revenue effect

Here's the payoff that makes elasticity the most practical idea in microeconomics. A price change pulls revenue (Price × Quantity) in two opposing directions: a higher price means more dollars per unit but fewer units. Which wins depends entirely on elasticity:

So the revenue-maximizing price sits exactly where demand turns from inelastic to elastic — at unit elasticity. Price below that and you're "leaving money on the table" (raise it); price above and you're choking volume (lower it). Let's see it concretely.

Part 4 — Worked example: NoteStack's demand curve

NoteStack's analysts estimate this monthly demand schedule (Q in thousands of subscribers):

The schedule follows a tidy rule: Q = 120 − 5P (every $1 price rise costs 5,000 subscribers). Notice what revenue does: it climbs to a peak of $720k at $12, then falls. That peak is the unit-elastic point.

Let's verify the elasticity at a couple of points using E = (ΔQ/ΔP) × (P/Q), where ΔQ/ΔP = −5:

• At $8 (Q=80): E = −5 × (8/80) = −0.5 → inelastic. Raising price from $8 would increase revenue (and indeed $8→$10 lifts revenue $640k→$700k). ✓
• At $12 (Q=60): E = −5 × (12/60) = −1.0 → unit elastic. Revenue is at its peak; nudging price either way barely changes it. ✓
• At $16 (Q=40): E = −5 × (16/40) = −2.0 → elastic. Cutting price from $16 would raise revenue. ✓

So if NoteStack only cared about revenue, it would price at $12. (We'll see in Lesson 2 that once you account for costs, the profit-maximizing price is a little different.) The lesson: the same product has elastic and inelastic regions, and smart pricing means knowing which one you're standing in.

Part 5 — Two more elasticities worth knowing

Price elasticity has cousins that explain customer behavior:

• Income elasticity — how demand responds to customers' income. Positive for normal goods (most things), strongly positive for luxuries (demand surges in booms, craters in recessions), and negative for inferior goods (instant noodles, discount brands — demand rises when incomes fall). This tells you how your sales will swing with the economy (a preview of Module 5).
• Cross-price elasticity — how demand for your product responds to a change in another product's price. Positive → the two are substitutes (NoteStack and JotBox: if JotBox raises prices, NoteStack gains). Negative → complements (printers and ink, consoles and games).

These let you anticipate ripple effects: a recession (income elasticity) or a competitor's price move (cross-price elasticity) will move your demand in predictable directions.

Key takeaways

• Price emerges where supply meets demand; managers should always ask which curve shifted and why before reacting.
• Price elasticity of demand = %ΔQ ÷ %ΔP — elastic (|E|>1) means quantity is very responsive; inelastic (|E|<1) means it isn't. Driven by substitutes, necessity, budget share, and time.
• Elasticity decides what a price change does to revenue: raise price when inelastic (revenue up), cut price when elastic (revenue up). Revenue is maximized at unit elasticity.
• NoteStack (Q = 120 − 5P) is unit-elastic at $12, where revenue peaks at $720k — inelastic below, elastic above.
• Income and cross-price elasticities predict how your demand moves with the economy and with rivals' prices.

Knowledge check

1. A product's demand is inelastic. If the company raises its price, what happens to unit sales and to total revenue?
2. Name two factors that tend to make a product's demand more elastic.
3. Using E = (ΔQ/ΔP)(P/Q) with ΔQ/ΔP = −5, compute NoteStack's elasticity at a price of $10 (Q = 70). Is it elastic or inelastic?
4. At what price does NoteStack's revenue peak, and what is the elasticity there?
5. Salt and a luxury cruise: which has inelastic demand and which has elastic demand, and why?

You now know how customers respond to price. But the revenue-maximizing price isn't the same as the profit-maximizing price — for that, we have to bring costs back in. Next: marginal thinking, and the rule that pins down the single best price.

→ Lesson 2: Costs, Margins & Optimal Pricing