Demand function

Demand function refers to a mathematical equation that describes the relationship between the quantity of a good demanded and its various determinants, such as price, income, and prices of related goods.
Updated: Jun 10, 2024

3 key takeaways

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  • A demand function expresses the quantity of a good demanded as a function of its price and other factors.
  • It helps in understanding how changes in determinants like price and income affect demand.
  • Economists use demand functions to predict consumer behavior and make informed market decisions.

What is a demand function?

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A demand function is a mathematical representation that shows the relationship between the quantity of a good or service demanded and its determining factors. The most common factors included in a demand function are the price of the good, consumer income, and the prices of related goods (substitutes and complements). The general form of a demand function can be written as:

[ Q_d = f(P, I, P_r) ]

where ( Q_d ) is the quantity demanded, ( P ) is the price of the good, ( I ) is consumer income, and ( P_r ) represents the prices of related goods.

The demand function helps economists and businesses understand how different variables affect consumer demand and predict changes in the market.

Factors included in a demand function

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  • Price of the Good (P): Typically, there is an inverse relationship between the price of the good and the quantity demanded. As the price increases, the quantity demanded decreases, and vice versa.
  • Consumer Income (I): The effect of income on demand can vary depending on the type of good. For normal goods, an increase in income leads to an increase in demand, while for inferior goods, an increase in income leads to a decrease in demand.
  • Prices of Related Goods (P_r): This includes both substitutes and complements. The demand for a good can increase if the price of a substitute rises or if the price of a complement falls.
  • Preferences and Tastes: Changes in consumer preferences can shift the demand function. For example, a trend or fad can increase demand for a particular good.
  • Expectations: If consumers expect prices to rise in the future, they may increase current demand. Similarly, if they expect prices to fall, they might decrease current demand.
  • Number of Buyers: The total number of consumers in the market also affects the overall demand for a good.

Types of demand functions

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  • Linear Demand Function: This is the simplest form of a demand function, represented as:
    [ Q_d = a – bP ]
    where ( a ) and ( b ) are constants. It shows a straight-line relationship between price and quantity demanded.
  • Non-linear Demand Function: More complex functions can capture more nuanced relationships. For example, a quadratic demand function might look like:
    [ Q_d = a – bP + cP^2 ]
  • Logarithmic and Exponential Functions: These forms can be used to model demand in cases where changes in demand are not proportional to changes in price or other variables.

Implications of the demand function

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  • Pricing Strategy: Businesses use demand functions to set optimal prices. Understanding how quantity demanded responds to price changes helps in maximizing revenue.
  • Market Analysis: Economists and market analysts use demand functions to predict consumer behavior and assess the impact of economic policies or market changes.
  • Policy Making: Governments use demand functions to understand how taxes, subsidies, or regulations will affect the demand for goods and services.

Examples and applications

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Consider a linear demand function for a product:
[ Q_d = 100 – 5P ]
This means that if the price is $10, the quantity demanded will be:
[ Q_d = 100 – 5(10) = 50 ]


  • Revenue Forecasting: Businesses can forecast revenues by understanding how changes in price affect demand.
  • Tax Impact Analysis: Policymakers can estimate the effects of new taxes on the consumption of certain goods.
  • Marketing Strategies: Companies can tailor their marketing strategies based on how sensitive demand is to various factors.

Understanding the demand function is essential for analyzing market dynamics, setting prices, and making informed business and economic decisions.

Sources & references
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Arti is a specialized AI Financial Assistant at Invezz, created to support the editorial team. He leverages both AI and the knowledge base, understands over 100,000... read more.