Tax Wedge vs Excess Burden of Taxation
Tax Wedge and Excess Burden of Taxation are two Public Finance & Taxation 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. Excess Burden of Taxation is the excess burden of a tax is the deadweight loss it creates beyond the revenue collected, arising because the tax distorts consumption and production decisions. 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.
A tax drives a wedge between the price buyers pay and sellers receive, shrinking the quantity traded below the efficient level and destroying mutually beneficial transactions. The lost surplus over and above the tax revenue is the excess burden, usually shown as the 'Harberger triangle'. Its size grows with the square of the tax rate and is larger when supply or demand is more elastic, which is why broad, low-rate taxes on inelastic bases are more efficient.
Tax Wedge vs Excess Burden: A Height and an Area
| Tax Wedge | Excess Burden of Taxation | |
|---|---|---|
| What it measures | A vertical distance, in dollars per unit, between two prices | An area, a total number of dollars of value destroyed |
| Where it sits on the diagram | The gap between demand and supply at the after-tax quantity | The triangle between the curves, from the new quantity out to the old one |
| Size when demand or supply is perfectly inelastic | Still the full tax per unit | Zero, because quantity does not change and no trade is lost |
| What it tells you | How far apart the two prices are pulled, which with elasticity shows who pays | How costly the tax is on top of the money it raises |
| Relation to revenue | Revenue is the wedge multiplied by the quantity still traded | A loss nobody collects, the government included |
| Effect of doubling the tax | Doubles, one for one | Roughly quadruples, since the triangle grows in both dimensions |
The wedge is a height, the excess burden is an area
Take an illustrative market where quantity demanded is 100 minus the price and quantity supplied equals the price. The two meet at a price of 50 and a quantity of 50. Now put a tax of 10 per unit on each sale. Buyers end up paying 55, sellers keep 45, and the quantity traded falls to 45. The wedge is 55 minus 45, which is 10, exactly the tax. Revenue is 10 times 45, which is 450. The excess burden is the triangle sitting over the 5 units that are no longer traded, one half times 10 times 5, which is 25. Two different objects, and only one of them is money that ends up somewhere. The 450 moves from buyers and sellers to the government. The 25 goes nowhere, because it is the value of trades both sides wanted at the old price and neither can now afford to make. Notice that the wedge on its own told us nothing about the size of that loss. What it did tell us is the split: the price buyers face rose by 5 and the price sellers receive fell by 5, an even division because demand and supply are equally responsive in this example. Practise that split at /calculate/tax-incidence.
Doubling the tax roughly quadruples the excess burden
Go back to the same illustrative market and double the tax to 20 per unit. Buyers now pay 60, sellers keep 40, and quantity falls to 40. The wedge has doubled to 20, as it must, since the wedge is the tax. Revenue rises from 450 to 800, which is less than double, because the base it is charged on has shrunk. The excess burden goes from 25 to one half times 20 times 10, which is 100. It has quadrupled. The reason is that the triangle grows in both dimensions at once. The larger tax makes it taller, and the same tax also drives quantity further from equilibrium, which makes it wider. For small taxes the loss is small enough that nobody bothers about it, and for large ones it grows faster than the money raised. That asymmetry sits behind the usual advice to spread a revenue target thinly over a broad base rather than piling it on a few goods, and behind the result that the damage is worst where buyers or sellers can most easily walk away. Where nobody can walk away, the loss is zero even though the wedge is the full tax. Run other numbers at /calculate/deadweight-loss.
Frequently asked questions
What is the difference between the tax wedge and the excess burden of a tax?
The tax wedge is the gap between the price buyers pay and the price sellers receive, measured in dollars per unit, while the excess burden is the value of the trades the tax destroys, measured as an area. The wedge always equals the tax per unit, but the excess burden depends on how far the quantity traded falls.
Can a tax have a wedge but no excess burden?
Yes, whenever the quantity traded does not change, which happens when demand or supply is perfectly inelastic. The two prices are still pulled apart by the full amount of the tax, but no mutually beneficial trade is given up, so the entire burden is revenue transferred to the government.
Why does the excess burden grow faster than the tax that causes it?
Because a larger tax raises the height of the lost-surplus triangle and also pushes quantity further from equilibrium, which widens its base. Both dimensions grow together, so the area rises roughly with the square of the tax while revenue rises by less.
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