Complement goods are two products typically consumed together, so when the price of one rises, demand for the other falls. They have a negative cross-price elasticity of demand.
Complement goods are products you tend to use together, where buying more of one pushes you to buy more of the other. Think coffee and sugar, cars and gasoline, or computers and software. The demand for one is tied to the demand for its partner.
The defining feature is a negative cross-price elasticity of demand. When the price of gasoline jumps, people drive less and buy fewer cars, so demand for cars falls even though the car's own price didn't change. That inverse relationship (price of good A up, quantity demanded of good B down) is what tells you two goods are complements rather than unrelated or substitutes.
Complement goods show up in Topic 5.4, Elasticity in Areas Other Than Price. This is the part of the course where you stop looking only at how a good's own price affects its demand and start measuring how it responds to other variables, like the price of a related good or a change in income.
Macro builds on this because demand shifts driven by complements feed into the bigger picture: how markets respond, how producers set prices across product lines, and how a shock to one good (an oil price spike) ripples into related markets. Recognizing complementary relationships helps you predict which way a demand curve shifts when conditions change.
Keep studying Principles of Macroeconomics Unit 5
Visual cheatsheet
view galleryCross-Price Elasticity of Demand (Unit 5)
This is the formula that proves two goods are complements: divide the percent change in quantity of one good by the percent change in price of another. A negative result means complements.
Substitute Goods (Unit 5)
Substitutes are the mirror image of complements. Where complements have negative cross-price elasticity, substitutes have positive cross-price elasticity because a price rise in one good pushes buyers toward the other.
Determinants of Elasticity (Unit 5)
Whether a good has close complements affects how responsive its demand is. A good locked into a complementary bundle behaves differently when prices shift across that bundle.
In coursework you'll most often see complements tested through cross-price elasticity problems. Expect to calculate a cross-price elasticity, get a negative number, and correctly label the goods as complements. Multiple-choice questions give you a scenario (price of gas rises, what happens to demand for SUVs) and ask which way the demand curve shifts. On free-response or short-answer questions, you may need to identify two goods as complements and explain the negative sign, then connect it to a demand-curve shift in a labeled graph.
Complements are used together, so a price increase in one lowers demand for the other (negative cross-price elasticity). Substitutes replace each other, so a price increase in one raises demand for the other (positive cross-price elasticity). The sign of the cross-price elasticity is the quick test.
Complement goods are products consumed together, like cars and gasoline or coffee and sugar.
Complements have a negative cross-price elasticity of demand: when one good's price rises, demand for the other falls.
The sign of the cross-price elasticity is how you tell complements (negative) from substitutes (positive).
A stronger complementary relationship shows up as a larger negative cross-price elasticity number.
A price shock to one good shifts the entire demand curve for its complement, not just a movement along it.
Complement goods are two or more products typically used together, where a rise in the price of one reduces demand for the other. Cars and gasoline are a classic example, and they have a negative cross-price elasticity of demand.
Yes. A negative cross-price elasticity is the defining sign of complements, because raising the price of one good lowers the quantity demanded of the other. A positive value would mean the goods are substitutes instead.
Complements are consumed together (negative cross-price elasticity), while substitutes can replace each other (positive cross-price elasticity). If a gas price hike lowers car demand, they're complements; if it raises demand for hybrids, those are substitutes.
Use cross-price elasticity of demand: divide the percent change in quantity demanded of good A by the percent change in price of good B. A negative result means the two goods are complements.
Demand for the complement falls and its demand curve shifts left. For example, if gasoline prices spike, people buy fewer cars, so the demand for cars drops even though car prices didn't change.