Elastic vs. Inelastic Demand: What's the Difference?

The Definitions

Demand is elastic when the percentage change in quantity demanded is larger than the percentage change in price — the absolute value of the elasticity is greater than one. Buyers are highly responsive: a modest price increase drives a proportionally bigger drop in purchases. Demand is inelastic when the percentage change in quantity is smaller than the percentage change in price, an absolute value below one. Buyers keep buying roughly the same amount even as the price moves. The dividing line is unit elastic, where the two percentage changes are equal and the elasticity equals one. Note that this is a comparison of percentage changes, not of raw units or of the steepness of a line.

The Revenue Consequence

This is the distinction's most practical payoff. When demand is elastic, cutting the price raises total revenue, because the gain in units sold outweighs the smaller margin per unit; raising the price lowers revenue. When demand is inelastic, the relationship reverses: raising price raises total revenue, because so few buyers leave. That is why a struggling airline discounts seats while a utility or a pharmaceutical firm with no close substitute can raise prices without losing much volume. It is also why excise taxes are commonly levied on goods with inelastic demand — the tax raises revenue without collapsing the quantity sold.

Examples and the Time Dimension

Gasoline in the short run is the classic inelastic good: commuters still need to get to work this week regardless of price. Over several years, though, the same demand becomes noticeably more elastic as people buy more efficient vehicles, move closer to work, or shift to transit. That illustrates the general rule that elasticity rises with the time allowed to adjust. Conversely, a single brand of bottled water faces highly elastic demand because a dozen near-identical substitutes sit on the same shelf, even though demand for drinking water as a category is extremely inelastic. Market definition, not the physical product, drives the number.

Two Common Mistakes

First, do not equate a steep line with inelastic demand as a general rule. On a straight-line demand curve, elasticity is not constant: it is elastic on the upper portion, unit elastic at the midpoint, and inelastic on the lower portion, even though the slope never changes. Slope and elasticity are different things. Second, remember that the two extreme cases are graphical special cases: perfectly inelastic demand is a vertical line, where quantity does not respond at all, and perfectly elastic demand is a horizontal line, where any price increase drives quantity demanded to zero — the demand curve faced by a single firm in perfect competition.