Skip to content
OverCalculator
  1. Home
  2. Financial
  3. Deadweight Loss Calculator
Financial

Deadweight Loss Calculator

Estimate deadweight loss as the triangular welfare loss from a price wedge and quantity change caused by taxes, controls, monopoly, or other distortions.

Published

Deadweight loss
Lost total surplus
$1.50
Price wedge
$0.10
Quantity change
30
Quantity change %
6%

Deadweight loss is one half of the price wedge times the quantity change: $0.10 × 30 ÷ 2.

$
$

Results update as you type.

Deadweight Loss Calculator

This calculator estimates deadweight loss, the welfare loss that appears when a market moves away from the quantity that would have been traded without a distortion. Enter the original price and quantity, then the new price and quantity after a tax, subsidy, price ceiling, price floor, monopoly markup, quota, externality policy, or other wedge. The result is the triangular lost surplus implied by the price gap and quantity gap.

Deadweight loss is different from the other microeconomics calculators in this batch. The consumer surplus calculator measures value buyers receive from trades that happen. The price elasticity of demand calculator and price elasticity of supply calculator measure responsiveness to price changes. This page measures the value destroyed when a wedge changes the number of trades or pushes activity away from the efficient point.

What deadweight loss means

In a competitive market, mutually beneficial trades continue until the marginal buyer’s willingness to pay roughly equals the marginal seller’s cost. Total surplus is the sum of consumer surplus and producer surplus from those trades. A distortion can block some trades where willingness to pay exceeds cost, or encourage trades where cost exceeds willingness to pay. The missing or inefficient value is deadweight loss.

The calculator uses the common triangle approximation:

deadweight loss=12×∣new price−original price∣×∣new quantity−original quantity∣\text{deadweight loss} = \frac{1}{2} \times |\text{new price} - \text{original price}| \times |\text{new quantity} - \text{original quantity}|

The absolute values match the compute logic. The result is positive whether the price rises or falls and whether quantity rises or falls. The tool is estimating the size of the welfare triangle, not deciding whether the policy is good or bad overall. A policy can create deadweight loss and still have other goals, such as raising revenue, reducing harmful consumption, supporting incomes, or correcting an externality.

Example: deadweight loss from a price floor

The default inputs are an original price of 1.00, a new price of 0.90, an original quantity of 500, and a new quantity of 530. The price gap is the absolute difference between 0.90 and 1.00, which is 0.10. The quantity gap is the absolute difference between 530 and 500, which is 30.

The calculator multiplies one half by 0.10 and by 30:

deadweight loss=12×0.10×30=1.50\text{deadweight loss} = \frac{1}{2} \times 0.10 \times 30 = 1.50

The output therefore shows a lost total surplus of 1.50, a price wedge of 0.10, a quantity change of 30, and a quantity change percentage of 6.00 percent because quantity rose from 500 to 530. This example could represent a subsidy-like movement or another wedge that lowers the observed price while increasing quantity. The formula reports only the triangular welfare size; it does not allocate gains and losses among buyers, sellers, taxpayers, or government.

If price moved from 20 to 25 and quantity fell from 10,000 to 8,000, the price wedge would be 5 and the quantity gap would be 2,000. Deadweight loss would be one half times 5 times 2,000, or 5,000. That is a much larger triangle because both the wedge and the quantity change are larger.

Where deadweight loss comes from

Taxes are the classic example. A per-unit tax can raise the price paid by buyers, lower the price received by sellers, or both. Quantity traded falls when some buyers whose willingness to pay exceeded sellers’ cost no longer trade after the tax wedge. Part of the old surplus becomes tax revenue, but the triangle from trades that disappear is deadweight loss.

Price controls can also create deadweight loss. A binding price ceiling can reduce quantity supplied and create shortages. A binding price floor can increase quantity supplied above quantity demanded, leaving inefficient surplus production or lost exchanges. Monopoly pricing creates another wedge: the firm restricts output below the competitive quantity to raise price, and the forgone trades generate lost surplus.

Subsidies can create deadweight loss too. They may increase quantity beyond the efficient point if the cost of extra production exceeds buyers’ willingness to pay. The calculator can handle price decreases and quantity increases because it uses absolute gaps. What changes is the story behind the wedge and who bears the cost.

Using the result carefully

The triangular formula assumes a roughly linear supply-and-demand area around the change. It is appropriate for introductory economics, quick policy comparisons, and back-of-the-envelope market analysis. If supply or demand curves are strongly curved, if the wedge varies by unit, or if there are external benefits and costs not captured in the price, a more detailed model may be needed.

The result’s unit is price times quantity. If price is dollars per ticket and quantity is tickets, deadweight loss is dollars. If price is euros per kilogram and quantity is kilograms, the result is euros. If price is an index and quantity is not a physical market unit, the result may be a useful relative measure but not a currency amount.

Elasticity affects the size of deadweight loss because elastic demand or supply usually means quantity changes more when a wedge appears. To understand those responsiveness inputs, use the price elasticity of demand calculator, price elasticity of supply calculator, or cross price elasticity calculator for substitution patterns. To inspect the buyer side of the surplus area, use the consumer surplus calculator.

Tips for better inputs

  • Use the same market definition before and after the distortion.
  • Enter price levels, not percentage price changes.
  • Enter quantities over the same time period.
  • Decide whether the original point is the efficient benchmark before calling the difference deadweight loss.
  • Do not confuse the welfare triangle with tax revenue, subsidy cost, or producer profit.

Sources

Frequently asked questions

What is deadweight loss?
Deadweight loss is the total surplus that disappears when a market distortion prevents mutually beneficial trades. It is not revenue collected by government or profit gained by sellers. It is the welfare value that no buyer, seller, or third party receives after quantity moves away from the efficient level.
Why does the formula divide by two?
In the simple supply-and-demand diagram, the lost welfare area is a triangle. The price wedge is one side and the quantity reduction or expansion is the other. Triangle area equals one half times base times height, so the calculator multiplies the two gaps and divides by two.
What counts as a price wedge?
A price wedge is the gap between the original price and the new price relevant to the distortion you are modeling. It may come from a tax, subsidy, price ceiling, price floor, quota, monopoly markup, external cost, or other policy or market force that separates marginal benefit from marginal cost.
Can deadweight loss occur when price falls?
Yes. A subsidy or binding price ceiling can move price downward while changing quantity. The calculator uses absolute price and quantity gaps, so it estimates the size of the welfare triangle whether price rises or falls. Interpretation depends on the policy and market context.
Is deadweight loss the same as tax revenue?
No. Tax revenue is a transfer from buyers or sellers to government. Deadweight loss is the surplus lost because some trades no longer happen, or because resources are pushed into inefficient trades. A tax can create both revenue and deadweight loss, but they are separate areas.
What units should I enter for quantity?
Use the same quantity unit before and after the distortion: units, tickets, tons, hours, subscriptions, or another market measure. The result is in price-unit times quantity-unit. Mixing monthly and annual quantities or retail and wholesale prices will make the welfare estimate misleading.

Related calculators

Time Value of Money CalculatorMove one lump sum between present and future value using periodic nominal or continuous compounding.Week-over-Week Growth CalculatorCalculate week-over-week growth, absolute change, following-to-initial ratio, and weekly compound growth for short-term metrics.Consumer Surplus CalculatorEstimate consumer surplus per unit, total buyer surplus, and the linear demand triangle between willingness to pay and market price.GDP Deflator CalculatorCalculate the GDP deflator from nominal GDP and real GDP, then compare it with a previous deflator to estimate economy-wide price inflation.Inflation CalculatorEstimate how an amount changes between years using an average annual inflation rate, including adjusted amount, dollar change, and total inflation factor.Price Elasticity of Supply CalculatorCalculate price elasticity of supply with midpoint or standard percentage changes and interpret how responsive producers are to price changes.

Deadweight Loss Calculator updated at