econ.studio

Glossary term

Deadweight Loss

The value lost when a market trades away from its efficient quantity — gains from trade that vanish under a tax, price control, or monopoly. The triangle of lost surplus at the heart of market-failure analysis.

Glossary

Deadweight Loss

Deadweight loss is value that simply disappears when a market does not trade the quantity it should. Imagine a tax on concert tickets: some shows that a venue was willing to host, and that fans were willing to attend, never happen because the tax pushes the effective price too far apart for both sides. Nobody keeps that lost value — the fans do not get the experience, the venue does not get the revenue, and the government collects nothing on those unbooked shows. It is simply gone.

More formally, deadweight loss is the reduction in total surplus — consumer surplus plus producer surplus — that occurs whenever the quantity traded is pushed away from the competitive equilibrium. A tax, a price ceiling, a price floor, a quota, or monopoly pricing can all cause this wedge. On a standard supply-and-demand diagram the deadweight loss appears as the triangle between the demand curve and the supply curve over the range of units that are no longer traded. The more elastic either supply or demand, the larger the drop in quantity and the bigger that triangle. You can explore how this triangle forms in the welfare section of the supply and demand model.

DWL=12×ΔQ×tax wedgeDWL = \tfrac{1}{2} \times \Delta Q \times \text{tax wedge}
deadweight-loss-triangle
ΔQ\Delta Q is the drop in quantity traded caused by the policy; the tax wedge is the gap it drives between the price buyers pay and the price sellers receive. Because the lost gains are triangular — they taper from the full wedge down to zero — the area is one-half base times height. Larger elasticities mean a larger ΔQ\Delta Q and a larger triangle.
Total surplus
The sum of consumer surplus and producer surplus, written CS+PSCS + PS. Total surplus is maximized at the competitive equilibrium and falls by the amount of the deadweight loss whenever output moves away from that point.
Tax wedge
The gap between the price buyers pay and the price sellers receive after a per-unit tax is imposed. A larger wedge depresses quantity more and generates more deadweight loss, even if it also raises more tax revenue on the units still traded.
Allocative efficiency
A market outcome is allocatively efficient when every unit whose value to buyers exceeds its cost to sellers is actually produced — that is, when deadweight loss is zero. The competitive equilibrium achieves allocative efficiency; taxes, quotas, and monopoly pricing do not.
Market equilibrium
The price and quantity at which the supply curve and demand curve intersect. At market equilibrium total surplus is at its maximum and deadweight loss is zero; any policy that forces the market away from this point creates a deadweight loss triangle.