Cross Elasticity of Demand

How one product's price moves another's sales

Cross elasticity of demand measures the ripple effect between two products: when the price of one good changes, how much does the demand for a different good change? It is calculated as the percentage change in quantity demanded of good A divided by the percentage change in the price of good B. The sign of the result reveals the relationship between the two products.

This sign is what makes the concept so useful. It tells economists, companies and investors whether two products compete with each other or are bought together.

Substitutes and complements

A positive cross elasticity means the goods are substitutes: when one gets pricier, people switch to the other, so its demand rises. If tea becomes expensive, coffee sales climb; if one airline hikes fares, a rival's bookings grow. The bigger the positive number, the closer the substitutes.

A negative cross elasticity means the goods are complements, bought and used together. When the price of one rises, demand for both falls. Cars and petrol, smartphones and data plans, printers and ink cartridges are classic complements; a jump in fuel prices dents car sales, and pricier cars dampen petrol demand.

When cross elasticity is near zero, the goods are unrelated, the price of salt has no bearing on demand for laptops.

Why it matters for business and investing

For companies, cross elasticity guides pricing and strategy. A firm whose product has close substitutes has little pricing power, raise prices and customers defect, which is why commoditised businesses struggle. A firm whose product complements a fast-growing one rides that growth: makers of EV-charging gear benefit as electric cars spread.

For investors, the concept sharpens competitive and thematic analysis. Understanding substitution explains why a company faces margin pressure when cheaper rivals emerge, and why some businesses have durable pricing power (few substitutes) while others don't. Recognising complements helps spot second-order plays on a trend, the picks-and-shovels suppliers that gain when a complementary product booms. It is a simple framework that quietly underpins how pricing power, competition and demand linkages shape the long-term fortunes of the companies a fund or investor owns.