Excess Profits Tax: History and Design

An excess profits tax is a levy on corporate earnings above a defined threshold of “normal” or baseline profitability, designed to recapture gains that arise from unusual market conditions or windfalls rather than efficient operation—a tool with roots in wartime finance and recent echoes in contemporary energy and pharmaceutical debates.

Wartime origins and the logic of abnormal gains

The excess profits tax first appeared in systematic form during the First World War. The U.S. introduced one in 1917 to capture windfalls earned by munitions makers, shipbuilders, and other defense contractors whose profits surged not from superior management but from government demand and restricted competition.

The underlying moral logic was plain: in normal times, a firm earns profit proportional to its capital and efficiency. Wartime scarcity, or a government monopoly on demand, inflates returns above what the business would earn in peace. Those excess gains belong to the public, not to shareholders who happened to own a firm in the right place at the right time.

The British employed a similar rationale. Between 1915 and 1921, the U.K. levied an excess profits duty that taxed net profits above a baseline—initially set as a return on pre-war capital or on average profits in the pre-war years. The tax funded the war effort and, as lawmakers saw it, prevented private profiteering on the nation’s peril.

This wartime precedent established a template: identify a baseline return, measure actual profits against it, and tax the difference at a high marginal rate.

Defining the baseline: the central puzzle

The core design challenge is always the same: how do you define “normal” profit?

Several approaches have been tried:

Prior-year averaging: Compare current profits to the average of the prior three or five years. A firm that earned £100 million annually in peacetime but £300 million during war pays tax only on the £200 million excess. Simple, but inflexible: a growing firm in peacetime may be penalized for legitimate expansion.

Statutory return rate: Set a fixed percentage return on capital or equity. For instance, “any profit above 10% of net assets is excess.” This works in stable environments but may be arbitrary. Is 10% normal for a bank? A tech startup? A utility?

Comparative peer benchmark: Tax a firm on profits above the median or average return of its peers. This captures the idea that excess is relative to industry norms. But it creates gaming incentives (firms lobby to be grouped with lower-return industries) and requires detailed competitive data that may not be transparent.

Statutory calculation: Define excess as profits above a notional “normal business return” set by statute, often adjusted for inflation, prevailing interest rates, or risk. This is precise but rigid and invites litigation over whether the statutory figure reflects economic reality.

Economic effects and unintended consequences

In theory, an excess profits tax leaves normal profits untouched and thus should not discourage ordinary investment or innovation. A firm earning its baseline return faces no higher marginal tax rate than under a standard corporate income tax.

But in practice, excess profits taxes distort behavior. A firm contemplating a new investment must weigh: if the project succeeds and generates “excess” returns, a portion goes to the state. The after-tax return on equity falls. The firm requires a higher pre-tax return to justify the capital outlay, raising the hurdle rate for marginal projects. Over time, less investment occurs.

Supply also responds. If an energy firm knows that unusually high oil prices will trigger a windfall tax, it may defer production to a later year when prices normalize. Sellers of goods face similar incentives: raise price during scarcity to lock in margin, but risk an excess profits tax. Some sellers may prefer to limit supply and avoid the tax threshold rather than maximize revenue. The net result: less supply, higher prices for consumers, and lower economic efficiency.

Labor also migrates. Excess profits taxes can be imposed selectively on certain industries (say, energy or pharmaceuticals) while others escape. Skilled workers and capital gravitate toward untaxed sectors, starving the taxed industry of resources. Over time, the taxed sector may underinvest, stagnate, and become less competitive globally.

The U.S. experience, 1917–1922 and 1940–1945

The first U.S. excess profits tax (1917–1921) raised substantial revenue but was widely viewed as arbitrary and complex. Defining a “normal” profit margin proved contentious. Firms with different capital structures or growth profiles claimed the baseline was unfair to them. Litigation proliferated. By the early 1920s, the tax was repealed as economic activity slowed and the political appetite for the tax waned.

The second U.S. excess profits tax (1940–1945) followed a similar arc. During World War II, the government wanted to ensure that defense contractors did not profiteer. The tax was applied with high rates and aimed to recapture all or most of extraordinary wartime gains. Again, defining the baseline consumed administrative resources and generated disputes. Many firms could claim they were reinvesting profits or facing unusual costs. The simplicity promised by the tax evaporated in practice.

Post-war, both taxes were allowed to expire. The consensus emerged that excess profits taxes, while politically popular in moments of crisis or public anger, are administratively cumbersome and economically inefficient.

Modern windfall-profit proposals

In recent decades, excess profits tax logic has resurged in specific circumstances. During the 1970s energy crisis, the U.S. briefly imposed a windfall profits tax on crude oil to capture a portion of the gain from price decontrol. The tax was intended to sunset but was repealed in 1988 as administering it proved complex and politically contentious.

More recently, proposals for “excess” or “windfall” taxes have focused on sectors where supply shocks or demand surges produce visible, concentrated profits. Energy companies during periods of high oil and gas prices; semiconductor firms during chip shortages; pharmaceutical companies with blockbuster drugs—all have faced calls for a windfall tax.

The modern design often sidesteps the “normal return” problem by simply defining excess as profits above a recent historical baseline (prior five-year average) or by capping the tax rate on profits above a specific monetary threshold per unit sold. The UK, for instance, imposed a windfall tax on energy companies in 2022, levying a 25% surcharge on profits above a specified baseline—a more administratively tractable approach than computing fair-return rates.

Why excess profits taxes recur despite history

Despite the cautionary history, excess profits taxes remain politically attractive because they feel just. When a firm earns extraordinary gains while consumers suffer—high gas prices, unaffordable drugs, wartime sacrifice—the impulse to tax away the windfall is visceral.

Economically, this impulse is not baseless. If the gains truly stem from a temporary or exogenous shock (a war, a natural disaster, a cartel collapse) rather than the firm’s own competitive advantage, a temporary tax may impose little cost. A firm with an unearned windfall faces no long-term disincentive to invest—it knows the tax is temporary and the baseline will not recur.

But distinguishing durable competitive advantage from temporary windfall is hard. Is a pharmaceutical firm’s blockbuster profit the result of R&D risk-taking and innovation, or a temporary monopoly of supply? Is an energy firm’s profit from drilling acumen, or from a geopolitical shock? Both stories have merit. Once a tax is in place, the firm cannot easily unwind its effect, and future decision-making is distorted regardless.

See also