Elasticity of demand measures how strongly buyers respond when the price of a good or service changes. It matters because the same price increase can cause a big drop in sales for one product but almost no change for another. Businesses use elasticity to set prices, predict revenue, and understand customers.
Consumers use the idea to see how budgets, substitutes, and needs shape buying choices.
The basic idea is to compare the percent change in quantity demanded with the percent change in price. If quantity changes a lot when price changes, demand is elastic. If quantity changes only a little, demand is inelastic.
Elasticity is especially useful in personal finance because it explains why people cut back quickly on snacks or streaming services but may keep buying gasoline, medicine, or basic groceries even when prices rise.
Key Facts
- Price elasticity of demand = percent change in quantity demanded / percent change in price
- Elastic demand means |elasticity| > 1, so quantity demanded changes by a larger percent than price.
- Inelastic demand means |elasticity| < 1, so quantity demanded changes by a smaller percent than price.
- Unit elastic demand means |elasticity| = 1, so percent change in quantity demanded equals percent change in price.
- Total revenue = price x quantity sold
- Goods with many substitutes, higher budget share, or more time to adjust usually have more elastic demand.
Vocabulary
- Elasticity of demand
- A measure of how much quantity demanded changes in response to a change in price.
- Quantity demanded
- The amount of a good or service consumers are willing and able to buy at a specific price.
- Elastic demand
- Demand is elastic when a price change causes a relatively large change in the quantity buyers purchase.
- Inelastic demand
- Demand is inelastic when a price change causes only a relatively small change in the quantity buyers purchase.
- Total revenue
- The money a seller receives from sales, found by multiplying price by quantity sold.
Common Mistakes to Avoid
- Ignoring percent changes and using only dollar changes is wrong because elasticity compares relative changes, not absolute changes.
- Forgetting that demand elasticity is usually negative is wrong because price and quantity demanded usually move in opposite directions, although economists often discuss the absolute value.
- Assuming all necessities are perfectly inelastic is wrong because even needed goods can become more elastic over time if people find substitutes or change habits.
- Thinking a price increase always raises revenue is wrong because if demand is elastic, the drop in quantity sold can be large enough to reduce total revenue.
Practice Questions
- 1 A movie ticket price rises from 12, and weekly tickets sold fall from 500 to 400. Using the simple percent change method based on the original values, calculate the price elasticity of demand.
- 2 A coffee shop lowers the price of a drink from 4, and the quantity sold rises from 200 to 260 per day. Calculate total revenue before and after the price change, then decide whether revenue increased or decreased.
- 3 A student buys the same amount of insulin after the price rises but buys fewer brand-name chips when their price rises. Explain which product likely has more inelastic demand and why.