What it means
The starting point is the law of demand: quantity bought moves in the opposite direction to price. The reasoning is that each extra unit gives a buyer less additional satisfaction than the one before, so they will only take more if it becomes cheaper.
Demand theory draws a sharp line between a movement along the demand curve and a shift of the whole curve. A price change moves you along the curve, while a change in income, tastes, population, expectations or the price of a substitute moves the entire curve left or right.
Elasticity is the part managers use most. It measures how sharply quantity responds to price, and whether a price rise raises or lowers total revenue depends entirely on whether demand is elastic or inelastic in that particular range.
Two further classifications matter commercially. Substitutes see their demand rise when a rival's price rises and complements see theirs fall, while normal goods gain from rising incomes and inferior goods lose from them.
The theory is a simplification and it makes no secret of that. Real buyers treat price as a quality signal, respond to framing and anchoring, buy out of habit and occasionally want a luxury more as it becomes dearer, which is why pricing teams pair the theory with live testing.
In practice
Real-world examples.
Example
A streaming service raises its monthly price by 12% and loses 4% of subscribers. Because demand proved inelastic at that price point, total revenue rose, and the finance team used the result to calibrate the next increase.
Example
A coffee shop sees sales jump when the competing cafe two doors down raises its prices. The two are close substitutes, so a price change at one shifts the whole demand curve facing the other.
Example
A discount supermarket gains market share during a downturn as households trade down from premium grocers. Its own basket behaves like an inferior good, with demand rising as incomes fall.
Formula
Calculation
A linear demand function is written Qd = a - bP, where a is the quantity buyers would take at a price of zero and b is how many units are lost for each dollar of price. Point elasticity = (change in quantity / change in price) x (price / quantity).
A speciality tea brand estimates monthly demand as Qd = 5,000 - 40P, with P measured in dollars per kilogram.
At $50: Qd = 5,000 - (40 x 50) = 5,000 - 2,000 = 3,000 kg, and revenue is 50 x 3,000 = $150,000.
At $60: Qd = 5,000 - (40 x 60) = 5,000 - 2,400 = 2,600 kg, and revenue is 60 x 2,600 = $156,000.
Elasticity at $50 is -40 x (50 / 3,000) = -0.67. Because that is smaller than 1 in size, demand is inelastic there and the theory predicts a price rise will increase revenue. The figures confirm it: revenue rises by 156,000 - 150,000 = $6,000 even though volume falls by 400 kg.Case study
Seen in the real world.
Vellum Press is a fictional independent publisher invented to show demand theory applied to a real decision. Its flagship hardback sold 4,000 copies a year at $28, producing revenue of 28 x 4,000 = $112,000, and the editorial team was convinced the price was as high as the market would bear.
A price test in two regions suggested that at $22 the title would sell around 6,400 copies. That implies a quantity increase of 2,400 / 4,000 = 60% against a price fall of 6 / 28 = 21.4%, an elasticity of about -2.8, which is firmly elastic. Revenue at the lower price would be 22 x 6,400 = $140,800.
With a unit production cost of $9, contribution rose from (28 - 9) x 4,000 = $76,000 to (22 - 9) x 6,400 = $83,200, so the cut improved profit as well as revenue. Vellum repriced the title, though it kept its poetry list unchanged after a separate test showed that segment was inelastic and a price cut there would simply have given away margin.
Watch out
Common mistakes.
- Assuming a price cut always raises revenue, when it only does so where demand is elastic in that particular range.
- Confusing a shift of the demand curve with a movement along it, and then blaming a pricing decision for what was really a change in the market.
- Applying one elasticity estimate across every product, region and season, when it varies sharply between them.
Questions
People also ask.
What is the difference between demand and quantity demanded?
Demand is the whole relationship between price and quantity, while quantity demanded is the single number that goes with one particular price.
Are there exceptions to the law of demand?
A few, including status goods bought partly because they are expensive and situations where a rising price is read as a signal of quality or of further rises to come.
How do I use this without an economics background?
Focus on two questions: how sensitive are my customers to price, and what would shift their willingness to buy regardless of what I charge.
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