How do you show and calculate the cost of a subsidy to the government on a diagram?

• →A subsidy is a payment made by the government to producers to lower their costs of production and increase market supply.
• →When a government grants a subsidy, the supply curve shifts right and the vertical distance between the original and new supply curves is the amount of the subsidy per unit.
• →This reduces the market price paid by consumers and increases the quantity supplied.
• →There are now two relevant prices: the lower price paid by consumers and the higher price effectively received by producers (the consumer price plus the subsidy per unit).
• →As a result, the total cost of the subsidy to the government is found by multiplying the subsidy per unit (the vertical distance between the original and new supply curves) by the new equilibrium quantity.
• →For example, if the subsidy per unit is £4 and the new equilibrium quantity is 500 units, the total government expenditure on the subsidy is £2,000.
• →Therefore, on a supply and demand diagram, the government's total subsidy cost is represented by the rectangle bounded by the original supply curve, the new supply curve, and the new equilibrium quantity on the horizontal axis. This is shown on the diagram below. The total cost of the subsidy is shown by combining the green and blue boxes.

Diagram: Open full diagram → Shows the downward shift in supply, the gap between consumer price and producer price, and how to calculate total government expenditure as a rectangle on the diagram.

• →The subsidy per unit is a vertical shift, not a horizontal one. The new supply curve sits directly below the original by the exact amount of the subsidy, and this vertical distance is what is used in the calculation — not the change in equilibrium price alone.
• →Consumers do not receive the full subsidy as a price reduction. The fall in consumer price is typically less than the subsidy per unit; producers retain a portion. The producer's effective price (what they receive) equals the new consumer price plus the subsidy per unit.
• →The area of the government cost rectangle uses the new quantity, not the old. Because the subsidy increases output, the relevant quantity for the cost calculation is the post-subsidy equilibrium quantity, which will be higher than the pre-subsidy quantity.
• →The government cost rectangle can be split. Part of the rectangle represents the benefit passed on to consumers (lower price) and part represents the gain to producers (higher effective price). Being able to identify both components precisely is essential at higher mark levels.
• →A subsidy corrects for negative externalities in consumption or positive externalities in production. Understanding why a government intervenes — typically to increase output of a merit good or to correct underproduction — places the calculation in its correct analytical context.

This question assesses a student's ability to apply diagrammatic and numerical analysis to government intervention in markets, specifically the use of subsidies as a policy tool. It draws on Edexcel spec point 1.2.9.a — which covers indirect taxes and subsidies as forms of government intervention — and requires students to move between a graphical representation and an arithmetic calculation, demonstrating understanding of how the subsidy cost is determined by both the per-unit value and the resulting quantity traded.

Examined 3 times across Edexcel since 2017.

The shift from a bare calculation to an explanation requiring a diagram in 2025 indicates that the concept has been tested at progressively greater depth over this period.

• →How Markets Work — understanding how the price mechanism operates is essential context for analysing what happens to price and quantity when a subsidy is introduced and why the government bears a cost in doing so.