In AP Microeconomics, taxes are mandatory payments to the government that change market outcomes. Per-unit taxes raise marginal cost and shift supply, shrinking quantity and creating deadweight loss, while lump-sum taxes only raise fixed costs and leave price and quantity unchanged in the short run.
Taxes are mandatory charges the government places on individuals and firms. In AP Micro, you mostly care about what a tax does to a graph, and the answer depends entirely on which kind of tax it is.
A per-unit tax (like $2 per pack of cigarettes) raises a firm's marginal cost, so it shifts supply (or MC) up by the tax amount. The result is a higher price for consumers, a lower net price for producers, less quantity traded, smaller consumer and producer surplus, government revenue, and usually deadweight loss. How that burden splits between buyers and sellers depends on the price elasticity of demand and supply (EK POL-4.A.1). A lump-sum tax (a flat fee no matter how much you produce) is the opposite. It does not touch marginal cost or marginal benefit at all, so it only raises fixed costs and average total cost (EK POL-4.A.2). Output and price stay the same in the short run; only profit shrinks. If a tax question feels confusing, ask one thing first: does this tax change the cost of producing one more unit? That single question sorts almost every tax problem on the exam.
Taxes live in Unit 6 (Market Failure and the Role of Government), Topic 6.4, under learning objectives 6.4.A (define government interventions in imperfect markets), 6.4.B (explain, with graphs, how policies alter outcomes in perfectly and imperfectly competitive markets), and 6.4.C (calculate those changes from a graph or table). This is where everything you learned earlier in the course gets stress-tested. You have to apply a tax to a perfectly competitive market, then to a monopoly, and explain why the effects differ. Taxes also connect Unit 6 backward to Unit 2 (supply shifts, elasticity, tax incidence) and to externalities, since a per-unit tax on pollution is the standard fix for negative externalities. If you can draw a taxed market correctly and label the deadweight loss, you've mastered one of the most reliably tested skills in AP Micro.
Keep studying AP® Microeconomics Unit 6
Per-Unit Tax (Units 2 & 6)
A per-unit tax is the workhorse tax of AP Micro. It shifts supply or MC upward by exactly the tax amount, which is why quantity falls and deadweight loss appears. Every tax graph you draw starts with this move.
Lump-Sum Tax (Unit 6)
The lump-sum tax is the trick-question tax. Because it doesn't change marginal cost, a profit-maximizing firm keeps producing the same quantity at the same price. Only fixed cost, ATC, and profit change.
Deadweight Loss (Units 2 & 6)
Taxes create deadweight loss when they push quantity below the efficient level. The twist in Topic 6.4 is that a tax on a monopoly, which already underproduces, behaves differently than a tax on a competitive market. Some exam questions even ask which structure loses the least.
Tax Incidence (Unit 2)
Who actually pays a tax has nothing to do with who writes the check. The more inelastic side of the market eats more of the burden. This elasticity logic from Unit 2 is baked directly into EK POL-4.A.1.
Tax questions show up as both MCQs and FRQ parts, and they almost always test the same core moves. You'll be asked to draw or read a graph showing a per-unit tax (new price consumers pay, net price firms receive, new quantity, government revenue rectangle, deadweight loss triangle), or to calculate those areas from given numbers (LO 6.4.C). A classic MCQ angle compares market structures, like asking how a tax on an oligopoly affects allocative efficiency and deadweight loss compared to perfect competition, or which structure suffers the least deadweight loss from a tax. The lump-sum trap is a perennial favorite: an FRQ will impose a lump-sum tax on a monopoly and ask what happens to price and quantity, and the credited answer is "nothing changes except profit." Pollution taxes also appear as the corrective policy for negative externalities, sometimes with follow-up questions about effects on output and employment. No released FRQ uses the bare word "taxes" as its focus, but per-unit and lump-sum tax setups are standard FRQ material.
A per-unit tax scales with output, so it raises marginal cost, shifts the supply/MC curve up, lowers quantity, and creates deadweight loss. A lump-sum tax is a flat fee regardless of output, so it raises only fixed cost and ATC. Marginal cost is untouched, which means the profit-maximizing quantity and price don't change in the short run. The fastest test: if the tax depends on how many units you sell, it's per-unit and the graph shifts; if it's one flat payment, it's lump-sum and only profit falls.
A per-unit tax shifts the supply (or MC) curve up by the amount of the tax, raising the price consumers pay, lowering the net price firms receive, and reducing equilibrium quantity.
A lump-sum tax changes only fixed costs and ATC, so a profit-maximizing firm's price and quantity stay the same in the short run; only profit falls.
Tax incidence depends on elasticity, and the more inelastic side of the market (buyers or sellers) bears the larger share of the tax burden.
Per-unit taxes create deadweight loss in competitive markets by pushing quantity below the efficient level, and government revenue equals the tax times the new quantity sold.
Taxes affect different market structures differently, so a tax on a monopoly or oligopoly interacts with the underproduction those structures already cause.
Per-unit taxes are also the standard corrective policy for negative externalities, like a pollution tax that forces firms to internalize external costs.
Taxes are mandatory government charges on firms or consumers that alter market outcomes. AP Micro focuses on two types: per-unit taxes, which shift supply and reduce quantity, and lump-sum taxes, which only raise fixed costs. They're tested in Topic 6.4 under learning objectives 6.4.A through 6.4.C.
No, not in the short run. A lump-sum tax doesn't change marginal cost or marginal benefit, so the MR = MC quantity stays exactly the same (EK POL-4.A.2). Price and quantity are unchanged; only fixed cost, ATC, and profit are affected. This is one of the most common trap questions on the exam.
A per-unit tax is charged on each unit sold, so it raises marginal cost, shifts supply up, lowers quantity, and creates deadweight loss. A lump-sum tax is one flat payment regardless of output, so it raises only fixed costs and leaves price and quantity alone. Ask whether the tax changes the cost of one more unit; that's the whole distinction.
Both, and the split depends on elasticity, not on who the tax is legally imposed on. The more inelastic side of the market bears more of the burden because it can't adjust as easily. If demand is perfectly inelastic, consumers pay the entire tax even when it's collected from producers.
No. Per-unit taxes usually create deadweight loss because they shrink quantity below the efficient level, but lump-sum taxes create none since quantity doesn't change. And a per-unit tax on a negative externality can actually reduce deadweight loss by moving output toward the socially optimal quantity.
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.
Review units, study guides, and course resources.
Check this vocabulary in multiple-choice context.
Apply key concepts in written AP responses.
Estimate the exam score you are working toward.
Review the highest-yield facts before practice.
Put the full course together before test day.