What Is Price Elasticity of Demand? Types and Factors

By Markets & Investing DeskUpdated Nov 10, 2026

Definition

Price elasticity of demand measures how much the quantity buyers want changes when price changes. It equals the percentage change in quantity demanded divided by the percentage change in price.

Key takeaways

Demand is elastic when the absolute value exceeds 1 and inelastic when it falls below 1.
Close substitutes, discretionary purchases, large budget shares and more time make demand more elastic.
Raising prices lifts total revenue when demand is inelastic and lowers it when demand is elastic.
A profit-maximizing monopolist always prices in the elastic part of its demand curve.

Price elasticity of demand (PED) measures how much the quantity of a good that buyers want changes when its price changes. It is the percentage change in quantity demanded divided by the percentage change in price. A result greater than 1 (in absolute value) means demand is elastic: buyers respond more than proportionally to the price move. A result less than 1 means demand is inelastic: quantity moves proportionally less than price.

What Is Price Elasticity of Demand?

The law of demand says that, other things equal, a higher price reduces the quantity demanded. Price elasticity of demand measures by how much. A 10% rise in the price of one coffee brand may send many shoppers to a competing brand. A 10% rise in the price of gasoline barely changes how much most drivers buy in the short run, because commuting, deliveries and flights still need fuel.

Because elasticity uses percentages, it is unit-free: the price sensitivity of milk measured in gallons can be compared with that of cars, or a price in dollars with one in euros.

How Price Elasticity of Demand Works

The basic formula is:

PED = (% change in quantity demanded) ÷ (% change in price)

Because a price increase normally causes a quantity decrease, the ratio comes out negative. A PED of −2 and a PED of 2 describe the same responsiveness, so this article, like most analyses, uses the absolute value.

The percentage (simple) method

The simplest approach measures each percentage change from the starting value:

% change in quantity = (new quantity − old quantity) ÷ old quantity
% change in price = (new price − old price) ÷ old price

Its weakness is that the answer depends on direction. Going from $4 to $5 is a 25% increase, but going from $5 back to $4 is a 20% decrease, so the same two points produce two different elasticities.

The midpoint (arc) method

To get one answer regardless of direction, economists often divide each change by the average of the old and new values:

% change in quantity = (Q₂ − Q₁) ÷ [(Q₁ + Q₂) ÷ 2]
% change in price = (P₂ − P₁) ÷ [(P₁ + P₂) ÷ 2]

The midpoint method gives the average elasticity over a stretch of the demand curve. For very small price changes, analysts use point elasticity, which multiplies the slope of the demand curve (ΔQ/ΔP) by the ratio P/Q at a specific point.

Interpreting Price Elasticity of Demand

Elasticity (absolute value)	Type	What a price change does
Infinite	Perfectly elastic	Any price increase drops quantity demanded to zero; the demand curve is horizontal
Greater than 1	Elastic	Quantity changes by a larger percentage than price
Exactly 1	Unit (unitary) elastic	Quantity changes by the same percentage as price
Less than 1	Inelastic	Quantity changes by a smaller percentage than price
0	Perfectly inelastic	Quantity does not change at all; the demand curve is vertical

A few readings:

PED of 2: price rises 5% and quantity falls 10%. The larger the number above 1, the stronger the reaction.
PED of 0.81: a 1% price increase reduces quantity demanded by about 0.81%. Demand is inelastic, though close to unit elastic.
Unit elastic everywhere: such a demand curve is not a straight line but a rectangular hyperbola, along which price times quantity stays constant.
Perfectly elastic: a theoretical benchmark for a single seller in a perfectly competitive market, where buyers can get an identical product at the market price.

Perfectly elastic and perfectly inelastic demand are mostly teaching limits; real goods fall between them.

Factors That Affect Price Elasticity of Demand

Elasticity depends on the buyer’s options and circumstances, which change over time.

Availability of substitutes

The easier it is to switch, the more elastic demand is. A shopper equally happy with coffee or tea will move to tea when coffee prices rise. Products without close substitutes, such as the one ink cartridge that fits a particular printer, tend to have inelastic demand.

Businesses reduce their own products’ price sensitivity through features, branding and loyalty, so customers see fewer acceptable alternatives when prices rise.

Necessity versus discretion

The more discretionary a purchase, the more elastic it tends to be. Someone whose washing machine still works can postpone a replacement if prices rise. Purchases that cannot wait, such as household heating or commuting fuel, respond less, and habit-forming products like cigarettes also show inelastic demand.

A price change on something that takes a small slice of income, such as salt or matches, barely registers, so demand tends to be inelastic. The same percentage change on a large expense, such as a car or rent, changes what a household can afford and draws a stronger response.

Time horizon and duration of the price change

Demand is usually more elastic in the long run than in the short run. Right after fuel prices jump, drivers have the same cars and the same commutes. Given more time, they can buy more efficient vehicles, carpool or move closer to work.

How long a price change lasts matters too. A one-day sale invites stockpiling, while a change that lasts a year changes habits. Seasonal swings may change little: swimsuits cost more in summer, but that is when people need them. Elasticity estimates are only comparable when their time frames match.

How broadly the market is defined

Demand for a broad category is less elastic than demand for one brand within it. Demand for food as a whole is very inelastic, while demand for a single brand of cereal can be quite elastic, because the other brands on the same shelf are close substitutes.

Example of Price Elasticity of Demand

Hypothetical example. A café sells 1,000 sandwiches a week at $4. It raises the price to $5, and weekly sales fall to 800.

Simple method (from the starting point):

Price change: ($5 − $4) ÷ $4 = 25%
Quantity change: (800 − 1,000) ÷ 1,000 = −20%
PED = −20% ÷ 25% = −0.8, or 0.8 in absolute value, which is inelastic

Midpoint method:

Price change: $1 ÷ $4.50 = 22.2%
Quantity change: −200 ÷ 900 = −22.2%
PED = −22.2% ÷ 22.2% = −1.0, which is unit elastic

The methods disagree because the simple method uses $4 and 1,000 as the base, while the midpoint method averages both ends. Revenue confirms the midpoint result: $4,000 before ($4 × 1,000) and $4,000 after ($5 × 800).

Why Is Price Elasticity of Demand Important?

Pricing and total revenue

Elastic demand (above 1): raising the price lowers total revenue, because the lost volume outweighs the higher price. Cutting the price raises revenue.
Inelastic demand (below 1): raising the price raises total revenue, because volume falls proportionally less than price rises.
Unit elastic demand (exactly 1): revenue stays the same.

Revenue is not profit. A price cut on an elastic product can raise revenue while lowering profit if the extra units cost more to produce than they bring in, so production costs belong in the same decision.

Monopoly pricing and markups

A firm with pricing power sets marginal revenue equal to marginal cost. Marginal revenue relates to elasticity through MR = P × (1 − 1/|PED|). When demand is inelastic, the term in parentheses is negative, so selling another unit lowers revenue. A profit-maximizing monopolist therefore always prices in the elastic part of its demand curve.

Rearranging gives the Lerner index, (P − MC) ÷ P = 1/|PED|. The less elastic the demand a firm faces, the larger the markup over marginal cost it can sustain. With a PED of 2, the profit-maximizing price is twice marginal cost; with a PED of 5, it is only 25% above it.

Taxes and public policy

A tax on a good with inelastic demand, such as tobacco or motor fuel, raises substantial revenue because consumption falls relatively little; a tax meant to discourage consumption works better on goods with more elastic demand. Elasticity also shapes tax incidence: the less elastic side of the market, buyers or sellers, bears more of the tax.

Limitations of Price Elasticity of Demand

It varies along the demand curve. On a straight-line demand curve, the slope is constant but elasticity is not. Demand is elastic at high prices and low quantities, unit elastic at the midpoint and inelastic at low prices and high quantities. One elasticity figure describes one range of prices, not the whole product.
It assumes other things stay equal. Real sales data mix price effects with changes in income, advertising, competitors’ prices, weather and seasons. Isolating the price effect takes careful statistical work, and estimates differ widely by method and data.
Estimates go stale. New substitutes, new technology or changing tastes can shift elasticity, so an old figure may not describe today’s buyers.
Nominal and real prices differ. A price increase that matches inflation is not a real increase. Analysts often adjust for inflation with a measure such as the Consumer Price Index before measuring buyer response.

Slope of the demand curve: slope measures absolute changes (units per dollar), while elasticity measures percentage changes. A steep curve is not automatically inelastic, and a flat one is not automatically elastic; the result depends on where on the curve you measure and on the units used.
Price elasticity of supply: measures how much the quantity sellers offer responds to price. It is usually positive, because higher prices encourage more production.
Income elasticity of demand: measures how quantity demanded responds to a change in buyers’ income rather than price. Positive values indicate normal goods; negative values indicate inferior goods.
Cross-price elasticity of demand: measures how demand for one good responds to the price of another. A positive value signals substitutes (coffee and tea), and a negative value signals complements (printers and ink).

FAQs

Is price elasticity of demand always negative?

Almost always, before the sign is dropped. The exceptions are theoretical cases such as Giffen goods, where a price rise increases quantity demanded, and they are rare enough that standard analysis treats the negative sign as given.

Can a product be elastic for one buyer and inelastic for another?

Yes. Elasticity describes how a group of buyers responds, and groups differ. Business travelers booking a flight tomorrow tend to respond less to fare changes than vacationers planning months ahead. Sellers use this difference to charge different prices to different customer groups, which is why fares vary by booking date and flexibility.

The Bottom Line

Price elasticity matters to businesses setting prices, policymakers designing taxes and anyone reading demand data. It shows whether a price change will raise or lower revenue, though production costs still decide profit. Treat any single estimate with care, because elasticity varies along the demand curve, shifts over time and depends on the method, data and time frame behind it.