Inelastic Demand: Definition, Formula, Curve, Examples

When Demand Pretty Much Stays the Same No Matter What Prices Do

Inelastic demand
If demand for something is perfectly inelastic, then the quantity purchased won't change no matter what the price is.

Definition: Inelastic demand in economics is when people buy about the same amount whether the price drops or rises. That happens with things people must have, like gasoline. Drivers must purchase the same amount even when the price increases. Likewise, they don't buy much more even if the price drops.  

Inelastic demand is one of the three types of demand elasticity. It describes how much demand changes when the price does.

The other two are:

  1. Elastic demand: When the quantity demanded changes more than the price does.
  2. Unit elastic demand: When the quantity demanded changes the same as the price.

Formula

You calculate demand elasticity by dividing the percent change in the quantity demanded by the percent change in the price. For example, if the quantity demanded changes the same percent as the price, the ratio would be one. If the price dropped 10 percent, and the quantity demanded increased 10 percent, then the ratio would be 0.1/0.1 = 1. The Law of Demand says that amount purchased moves inversely to price. That means you can ignore the plus and minus signs. That is called unit elastic.

Elastic demand is when the quantity to price ratio is more than one. That means if the price dropped 10 percent, and the amount demanded rose 50 percent, then the ratio would be 0.5/0.1 = 5.

At the other extreme, if the price dropped 10 percent and the quantity demanded didn't change, then the ratio would be 0/0.1 = 0.

That is known as being perfectly inelastic. It occurs when the ratio of quantity demanded to price is between zero (perfectly inelastic) and one (unit elastic).

For example, beef prices in 2014 rose 28 percent, but demand only fell 14.9 percent. This link takes you to the demand schedule.

Inelastic Demand Curve

You can also tell whether the demand for something is inelastic by looking at the demand curve.

Since the quantity demanded doesn't change as much as the price, it will look steep. In fact, it will be any curve that is steeper than the unit elastic curve, which is diagonal.

The more inelastic the demand, the steeper the curve. If it's perfectly inelastic, then it will be a vertical line. That's because the quantity demanded won't budge, no matter what the price is. That's shown in the chart above. 

Five factors determine demand for each individual. They are price, the price of alternatives, income, tastes and expectations. For aggregate demand, the sixth determinant is number of buyers. The demand curve only shows how the quantity changes in response to price. If one of the other determinants change, it will shift the entire demand curve. That means more (or less) will be demanded, even though the price remains the same.

Examples

There is no example in real life of something with perfectly inelastic demand. If that were the case, then the supplier could charge an infinite amount, and people would have to buy it.

The only thing that would come close would be if someone managed to own all the air, or all the water, on Earth. There is no substitute for either. People must have air and water, or they die in a short period. Even that's not perfectly inelastic. That's because the supplier couldn't charge 100 percent of the income in the world. People would still need some money for food, or they'd starve within a few weeks. It's hard to imagine a situation that would create perfectly inelastic demand.

But some products come close. For example, gasoline is something that drivers need a certain amount of each week. Gas prices change every day. If there is a drop in supply, the prices will skyrocket. For example, that's what happened during the OPEC oil embargo in 1973.

People will still buy gas because they can't immediately change their driving habits. To shorten their commute time, they'd need to change jobs. They'd still need to get groceries at least weekly. They could go to a store that's closer, if possible. But most people would tolerate higher gas prices before they would make such drastic changes. You can see how that would cause demand-pull inflation.

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