How do elasticities decide who really pays a tax and how policy bites?
Apply elasticity concepts to the incidence of taxes and subsidies and to firm and government decisions
A focused answer to the H2 Economics learning outcome on applying elasticity. How PED and PES split the incidence of a tax or subsidy, and how elasticities shape pricing, taxation and policy decisions.
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What this dot point is asking
SEAB wants you to apply elasticity to real decisions, above all the incidence of an indirect tax or subsidy (who actually bears it) and how elasticity shapes firm pricing and government policy. The central insight is that elasticity decides who pays and how hard a policy bites, so it is the single most powerful evaluation tool in microeconomics.
The answer
Tax incidence: who really pays
An indirect tax (a per-unit or ad valorem tax on a good) shifts the supply curve upward (leftward) by the amount of the tax. The equilibrium price rises and quantity falls. But the price rarely rises by the full tax, so the burden is split. The split, the incidence, depends on relative elasticities.
The extreme cases make this vivid:
- Perfectly inelastic demand: consumers bear the entire tax; price rises by the full amount and quantity is unchanged.
- Perfectly elastic demand: producers bear the entire tax; price cannot rise at all.
Subsidy incidence: who really benefits
A subsidy shifts supply rightward (downward) by the amount of the subsidy, lowering price and raising quantity. By the same logic, the benefit goes mostly to the more inelastic side: if demand is inelastic, consumers gain most of the lower price; if demand is elastic, producers keep most of the subsidy.
Elasticity and government revenue
Tax revenue equals the tax per unit times the quantity sold after the tax. Because quantity falls less when demand is inelastic, inelastic goods raise the most revenue for a given tax. This is why governments levy heavy duties on tobacco, alcohol and fuel: demand is inelastic, so revenue is large and stable. But the same inelasticity means the tax does little to cut consumption, so a revenue aim and a consumption-reduction aim can pull in opposite directions.
Elasticity in firm decisions
Firms use PED to set prices (cut price for elastic goods, raise it for inelastic ones to grow revenue), use XED to price relative to substitutes and complements, and use YED to forecast how demand will move as incomes change. PES tells a firm and a regulator how quickly the market can respond to a price change.
Examples in context
Example 1. Singapore's fuel duty and COE. Petrol duty falls on a good with fairly inelastic short-run demand, so it raises substantial revenue while only modestly curbing driving in the short run; over the long run, as households adjust vehicle choices, demand becomes more elastic. The COE works on the quantity side, capping car numbers directly, an example of using inelastic willingness to pay to ration a fixed supply.
Example 2. Sugar and demerit-good taxes. A tax on sugary drinks aims to cut consumption, so its effectiveness depends on PED. Where close unsweetened substitutes exist, demand is fairly elastic and the tax (or reformulation it encourages) cuts sugar intake meaningfully; where demand is inelastic, the tax mainly raises revenue, which is why such policies are often paired with reformulation incentives.
Try this
Q1. A tax is placed on a good with perfectly inelastic demand. Who bears it and why? [2 marks]
- Cue. Consumers bear the entire tax: with perfectly inelastic demand, quantity does not fall, so the price rises by the full tax and producers pass it all on.
Q2. Explain why governments tax inelastic goods to raise revenue. [3 marks]
- Cue. Revenue is the tax per unit times quantity sold; with inelastic demand, quantity falls only a little after the tax, so a large quantity is still taxed and revenue is high and stable.
Q3. Why might a tax fail to cut consumption of an addictive good much? [2 marks]
- Cue. Addictive goods have inelastic demand, so even a sizeable price rise reduces quantity demanded only slightly, leaving consumption little changed in the short run.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original10 marksUsing elasticity, explain how the burden of an indirect tax is shared between consumers and producers, and why this matters for government revenue.Show worked answer →
A 10 mark question rewards the incidence rule tied to relative elasticities and the revenue implication.
- Incidence and elasticity
- An indirect tax shifts supply left, raising price and lowering quantity. The split of the tax between consumer and producer depends on relative elasticities.
- Inelastic demand
- If demand is more inelastic than supply, consumers bear most of the tax: price rises by most of the tax and quantity falls little, so the consumer share is large.
- Elastic demand
- If demand is more elastic than supply, producers bear most of the tax: consumers resist a higher price, so the price rises little and producers absorb most of it.
- Revenue
- Tax revenue is the tax per unit times the quantity sold. It is largest when demand (and supply) are inelastic, because quantity falls little, which is why governments tax inelastic goods such as tobacco and fuel to raise revenue reliably.
Markers reward the supply-shift mechanism, the relative-elasticity rule for who bears the tax, and the inelastic-goods-raise-more-revenue conclusion.
Original9 marksDiscuss how a government should use elasticity estimates when deciding whether to tax a demerit good to reduce its consumption.Show worked answer →
A 9 mark discuss question rewards the elasticity logic for consumption reduction, the revenue trade-off, and evaluation.
- Reducing consumption
- To cut consumption sharply, the tax works best where demand is elastic, because a given price rise then cuts quantity a lot. For an inelastic demerit good (such as cigarettes), a tax cuts consumption only modestly.
- The revenue trade-off
- With inelastic demand the tax raises a lot of revenue but reduces consumption little; with elastic demand it cuts consumption more but raises less revenue. The two aims can conflict.
- Evaluation
- For an addictive demerit good with inelastic demand, a tax alone is a weak consumption tool, so it should be combined with measures that shift demand left (education, advertising bans) or make demand more elastic over time. The tax still has merit for revenue and for deterring new users, who are more price-sensitive.
Markers reward the elastic-demand-for-bigger-consumption-cut logic, the revenue-versus-consumption trade-off, and a supported policy judgement that combines instruments.
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