Tax Wedge vs Tax Incidence
Tax Wedge and Tax Incidence are related concepts in AP Economics that students often mix up. A tax wedge is the gap a per-unit tax drives between the price buyers pay and the price sellers receive, equal to the tax per unit at the new quantity. Tax incidence refers to the distribution of the tax burden between buyers and sellers. Here is how they compare side by side.
When a tax is imposed, buyers pay one price and sellers keep a lower one; the vertical distance between them is the wedge, equal to the tax per unit. The wedge reduces the quantity traded below the efficient level and creates deadweight loss (the triangle whose base is the lost quantity and height is the wedge). How the wedge splits into buyer and seller burden depends on relative elasticities, but the size of the wedge itself equals the statutory tax per unit regardless of who legally pays it.
The incidence of a tax depends on the relative elasticities of supply and demand. If demand is more inelastic than supply, consumers bear a larger share of the tax burden. If supply is more inelastic than demand, producers bear a larger share.
Tax Wedge vs Tax Incidence: The Size of the Gap and the Split of the Gap
| Tax Wedge | Tax Incidence | |
|---|---|---|
| Type of quantity | One number, in dollars per unit | Two shares that must add up to that one number |
| What fixes its size | The statutory tax per unit, nothing else | Relative elasticity of demand and supply, nothing else |
| If the tax per unit doubles | Doubles exactly, since the wedge is the tax | Unchanged, straight-line curves hold the buyer and seller shares in the same ratio |
| If the law switches who remits the tax | Identical, a different curve shifts but the gap between the two prices does not change | Identical, legal responsibility and economic burden are separate questions |
| Link to deadweight loss | Direct input, deadweight loss = ½ × wedge × the fall in quantity | No effect on the size of the loss, only on which side gives up the surplus |
| How to read it off a diagram | Measure the vertical gap between demand and supply at the after-tax quantity | Split that gap at the original equilibrium price, the part above is the buyers' share and the part below is the sellers' |
| What a free-response prompt asks | State the tax per unit, or shade revenue as tax × after-tax quantity | Say which side bears more and justify it with relative elasticity |
Same tax, same wedge, same deadweight loss, and yet the burden flips
Two markets, both starting at Q = 20 and P = $50, both hit with the same $6 per-unit tax. In the first, demand is P = 90 - 2Q and supply is P = 30 + Q. After the tax, quantity falls to 18, buyers pay $54, and sellers keep $48, so buyers carry $4 of the $6 and sellers carry $2. In the second, demand is P = 70 - Q and supply is P = 10 + 2Q. Quantity again falls to 18, but now buyers pay $52 and sellers keep $46, so the shares reverse. Everything the wedge governs is identical across the two markets: the gap is $6, quantity drops by 2 units, revenue is $6 × 18 = $108, and deadweight loss is ½ × $6 × 2 = $6. Only the incidence moved, because the steeper and therefore less elastic side switched from demand to supply. The wedge is fixed by the legislature. The split is fixed by the curves.
Who writes the check is not who pays the tax
Levy the $6 on sellers and the supply curve rises by $6. Levy the same $6 on buyers and the demand curve falls by $6 instead. The two pictures look different and the arithmetic lands in the same place: same quantity, same $6 gap, same prices for buyers and sellers, same revenue, same deadweight loss. Statutory incidence, meaning who is legally required to remit the money, has no effect on economic incidence, meaning who ends up with less surplus. Free-response answers lose points here in a predictable way. The prompt says a tax is imposed on producers, and the response concludes that producers therefore bear it. The correct move is to ignore the legal side entirely and compare elasticities. If demand is relatively more inelastic than supply, buyers bear the larger share no matter who hands the money to the government. The wedge is the first thing you can write down, and the incidence is the last.
Frequently asked questions
Can buyers bear the entire tax wedge?
Buyers absorb the whole wedge when demand is perfectly inelastic or supply is perfectly elastic. Take the same $6 tax with a vertical demand curve at Q = 20. The price buyers pay rises from $50 to $56, sellers still keep $50, quantity does not move, revenue is $6 × 20 = $120, and deadweight loss is zero because no trades were lost. The extreme case is worth memorizing, since it shows the wedge and the incidence coming apart completely, and it explains why taxes on highly inelastic goods raise the most revenue per unit of efficiency sacrificed.
Is the tax wedge the same thing as deadweight loss?
Tax wedge and deadweight loss are different quantities that meet inside the same formula. The wedge is measured in dollars per unit and equals the tax. Deadweight loss is measured in total dollars and equals ½ × wedge × the fall in quantity, so it depends on how much trade the tax destroys. A $6 wedge in a market where quantity falls by 2 units produces $6 of loss, while the same $6 wedge in a market where quantity does not move produces none at all.
How do you find tax incidence on a graph?
Tax incidence is read off the vertical wedge, split at the original equilibrium price. The distance from the old price up to the new price buyers pay is the buyers' share. The distance from the old price down to the price sellers keep is the sellers' share, and the two must add to the tax per unit. Before measuring anything, check which curve is steeper near equilibrium, because the steeper, less elastic side always takes the larger piece.
Live Supply and Demand graph. Drag the curves, or open the full version.
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