Free deadweight loss calculator

What is deadweight loss?

Deadweight loss is the value lost to society when a market produces less than the efficient quantity. In a free, competitive market, every trade where a buyer values the good more than it costs to make actually happens — total surplus is maximised. When a tax, price control, subsidy, or monopoly pushes the market away from that equilibrium, some of those mutually beneficial trades stop happening. The surplus they would have created is not transferred to anyone — it simply disappears. That vanished surplus is the deadweight loss, and it is the number this deadweight loss calculator returns the moment you enter the original and new price and quantity.

Economists also call it the excess burden or welfare loss. On a supply-and-demand graph it shows up as a triangle wedged between the supply and demand curves, bounded by the efficient quantity on one side and the reduced quantity on the other — which is why it is often called the welfare-loss triangle. The calculator measures the area of that triangle.

The deadweight loss formula

Because the lost surplus forms a triangle, you find it with the area-of-a-triangle rule — one-half times base times height. The base is the change in quantity (the units no longer traded) and the height is the change in price (the gap the distortion opens between what buyers pay and what sellers receive).

This is the standard linear triangle approximation taught in introductory microeconomics and used by Omni Calculator and Corporate Finance Institute. It assumes the supply and demand curves are straight lines over the relevant range, so the lost-surplus area is a clean triangle. Take absolute values of both changes so the result is always a positive amount of lost welfare, whatever the direction of the move.

How to calculate deadweight loss

Calculating deadweight loss is a three-step process once you know the market's two states — the efficient outcome and the distorted one. The calculator above runs all three live as you type, but here is the logic behind it.

1. Find the change in quantity. Subtract the new quantity from the original efficient quantity and take the absolute value. This is the triangle's base — the trades that no longer happen.
2. Find the change in price. Subtract the new price from the original price and take the absolute value. This is the triangle's height — the wedge the tax, control, or monopoly drives between buyer and seller.
3. Multiply and halve. Multiply the base by the height and divide by two. The result is the deadweight loss — the dollar value of welfare destroyed.

A worked example using the deadweight loss calculator

Step 1 — Find the change in quantity (the base)

Quantity falls from 1,000 to 850 units, so |850 − 1,000| = 150 units. Those 150 trades no longer happen because of the tax — that is the base of the welfare triangle.

Step 2 — Find the change in price (the height)

Price rises from $10 to $13, so |13 − 10| = $3. That $3 is the tax wedge — the gap between what buyers now pay and what the market would have charged. It is the height of the triangle.

Step 3 — Multiply and halve

Half of base times height gives the deadweight loss.

What causes deadweight loss?

Deadweight loss appears whenever something stops the market from reaching its efficient quantity. Five distortions account for almost every real-world case:

1. Taxes. A tax raises the price buyers pay and lowers the price sellers keep, so fewer units trade. The tax revenue is a transfer, but the units that vanish are pure deadweight loss.
2. Price ceilings. A maximum price set below equilibrium (rent control, for example) makes the good cheap but scarce — sellers supply less than buyers want, and the unmet demand is lost surplus.
3. Price floors. A minimum price set above equilibrium (a minimum wage or an agricultural support price) creates a surplus the market cannot clear, so some efficient trades never occur.
4. Monopoly. A monopolist restricts output and charges above marginal cost to maximise profit. Customers who value the good above its true cost are priced out — their lost surplus is the monopoly deadweight loss.
5. Subsidies. A subsidy can push output above the efficient level, so units are produced whose cost exceeds the value buyers place on them. Over-production wastes resources just as under-production wastes trades.

The welfare-loss triangle explained

Picture the standard supply-and-demand diagram. The downward-sloping demand curve and the upward-sloping supply curve cross at the efficient equilibrium — the efficient price P1 and efficient quantity Q1. Everything trades, and total surplus (consumer surplus above the price plus producer surplus below it) is as large as it can be.

Now drive a wedge into the market — a tax, a price control, or a monopoly mark-up. Quantity falls to Q2, and a gap of |P2 − P1| opens between the price buyers pay and the price sellers receive. The deadweight loss is the triangle bounded by the demand curve on top, the supply curve on the bottom, and the vertical line at the new lower quantity Q2 on the right. Its base sits along the quantity axis — the distance Q1 − Q2 — and its height is the price wedge P2 − P1.

• The base is the quantity that disappears — every unit between Q2 and Q1 that would have been a mutually beneficial trade.
• The height is the price wedge — how far the distortion separates buyers' willingness to pay from sellers' willingness to accept on that last lost unit.
• The area (½ × base × height) is the surplus those lost trades would have created — gone, captured by no one.

That is why the formula is simply the area of a triangle: the lost-surplus region between the two curves is, under the linear approximation, a triangle with that base and that height.

Consumer surplus, producer surplus, and total welfare

Deadweight loss only makes sense against the idea of surplus. Surplus is the gain each side of a trade walks away with, and an efficient market maximises the sum of the two.

The key distinction is between a transfer and a loss. When a tax is imposed, part of the old consumer and producer surplus becomes government revenue — that is a transfer, not a loss; someone still has it. But the surplus from the trades that no longer happen is captured by nobody. That second piece is the deadweight loss, and it is what separates a distortion that merely redistributes wealth from one that genuinely shrinks the economic pie.

Deadweight loss in a monopoly

Monopoly deadweight loss is the most common exam and interview case, and it works a little differently from a tax. A competitive market produces where price equals marginal cost. A monopolist instead produces where marginal revenue equals marginal cost — a lower quantity — and charges the higher price the demand curve will bear at that quantity.

The result: output is restricted below the efficient level, and customers who would have paid more than it costs to serve them are shut out. The deadweight loss is the triangle between the competitive quantity and the monopoly quantity. To measure it with this calculator, set P1 and Q1 to the competitive price and quantity (where price equals marginal cost) and P2 and Q2 to the monopoly price and the lower quantity it sells. The classic textbook illustration is a producer whose nails cost about $0.10 each in a competitive market but who charges $0.60 as a monopolist, excluding every buyer who valued a nail between those two figures.

Why deadweight loss matters

Deadweight loss is how economists put a price on inefficiency. It turns an abstract claim — 'this policy distorts the market' — into a dollar figure you can weigh against the policy's benefits.

• Tax policy. Two taxes raising the same revenue can have very different deadweight losses. A tax on an inelastic good (where quantity barely moves) wastes far less than one on an elastic good — the logic behind taxing necessities like fuel and tobacco.
• Regulation. Price ceilings and floors trade efficiency for a distributional goal. Deadweight loss measures what that goal costs in lost trades, so the trade-off can be made with eyes open.
• Antitrust. The deadweight loss of monopoly is the core economic case for competition policy — it quantifies the surplus a dominant firm destroys by restricting output.

Limitations and common mistakes

• It is a linear approximation. The ½ × base × height formula assumes straight-line supply and demand. Real curves bend, so for large distortions the triangle is an estimate, not an exact figure.
• You need the efficient benchmark. The result is only as good as your P1 and Q1. Using the already-distorted price as the starting point understates the loss.
• Don't confuse the loss with the tax revenue. The tax collected is a transfer that still benefits someone; only the triangle is true deadweight loss. They are different areas on the graph.
• It ignores externalities. When a market has a negative externality (pollution, say), a tax can reduce deadweight loss by correcting the market — the simple triangle then tells only half the story.

Method and sources

This calculator computes deadweight loss with the linear welfare-triangle method, the standard taught in introductory microeconomics: DWL = ½ × |Q2 − Q1| × |P2 − P1|, where (P1, Q1) is the efficient equilibrium and (P2, Q2) is the distorted outcome. It is the same formula used by Omni Calculator and Corporate Finance Institute. As an illustration, CFI's organic-apples subsidy case — price moving from $1.00 to $0.90 as quantity rises from 500 million to 530 million pounds — yields a deadweight loss of about $1.5 million.

Calculators that work alongside the deadweight loss

These pair naturally with this one for decisions that sit nearby.

Frequently asked questions about the free deadweight loss calculator

About this deadweight loss calculator

This deadweight loss calculator runs entirely in your browser. Every figure you enter stays on your device — nothing is sent to a server, logged, or shared. It applies the linear welfare-triangle method, deadweight loss = ½ × |Q2 − Q1| × |P2 − P1|, taking the change in quantity as the triangle's base and the change in price as its height, and updates instantly as you type.

Calculators Cloud offers 400+ free tools with no sign-up. The whole Finance calculators shelf includes Price elasticity of demand, Marginal cost, and Marginal revenue tools alongside this one. Or browse the full calculator directory.