How A Tax Affects Market Participants

Now let's use the tools of welfare economics to measure the gains and losses from a tax on a good. To do this, we must take into account how the tax affects buyers, sellers, and the government. The benefit received by buyers in a market is measured by consumer surplus—the amount buyers are willing to pay for the good minus the amount they actually pay for it. The benefit received by sellers in a market is measured by producer surplus—the amount sellers receive for the good minus their costs. These are precisely the measures of economic welfare we used in Chapter 7.

What about the third interested party, the government? If T is the size of the tax and Q is the quantity of the good sold, then the government gets total tax revenue of T X Q. It can use this tax revenue to provide services, such as roads, police, and public education, or to help the needy. Therefore, to analyze how taxes affect economic well-being, we use tax revenue to measure the government's benefit from the tax. Keep in mind, however, that this benefit actually accrues not to government but to those on whom the revenue is spent.

Figure 8-2 shows that the government's tax revenue is represented by the rectangle between the supply and demand curves. The height of this rectangle is the size of the tax, T, and the width of the rectangle is the quantity of the good sold, Q. Because a rectangle's area is its height times its width, this rectangle's area is T X Q, which equals the tax revenue.

Welfare without a Tax To see how a tax affects welfare, we begin by considering welfare before the government has imposed a tax. Figure 8-3 shows the supply-and-demand diagram and marks the key areas with the letters A through F.

Without a tax, the price and quantity are found at the intersection of the supply and demand curves. The price is P1, and the quantity sold is Q1. Because the demand curve reflects buyers' willingness to pay, consumer surplus is the area between the demand curve and the price, A + B + C. Similarly, because the supply curve reflects sellers' costs, producer surplus is the area between the supply curve and the price, D + E + F. In this case, because there is no tax, tax revenue equals zero.

Total surplus, the sum of consumer and producer surplus, equals the area A + B + C + D + E + F. In other words, as we saw in Chapter 7, total surplus is the area between the supply and demand curves up to the equilibrium quantity. The first column of Table 8-1 summarizes these conclusions.

Figure 8-3

How a Tax Affects Welfare. A tax on a good reduces consumer surplus (by the area B + C) and producer surplus (by the area D + E). Because the fall in producer and consumer surplus exceeds tax revenue (area B + D), the tax is said to impose a deadweight loss (area C + E).


Price buyers : pay

Price without tax

Price sellers : receive


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  • lillian
    How tax affect market participation?
    24 days ago

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