What it means
Natural monopolies, such as water and electricity networks, exist because one provider serves a market more cheaply than several could. Left alone, that single provider would restrict output and charge monopoly prices, so regulators choose the price instead.
The average cost pricing rule is one of their standard answers. The rule works by finding the point where the average cost curve meets the demand curve.
At that price and quantity, revenue exactly covers total cost per unit, including a fair return on invested capital, so the monopoly survives without subsidy while customers pay far less than the unregulated monopoly price. Standard economics textbooks present the rule as the middle path among regulatory choices.
Forcing the firm to price at marginal cost, the economically ideal output, can push price below average cost when costs are falling and bankrupt the utility. Average cost pricing sacrifices some efficiency to keep the lights on, literally.
On the regulator's graph, monopoly output is small and expensive, marginal-cost output is large but loss-making, and average-cost output sits between the two, so society accepts slightly too little output in exchange for a solvent provider. Modern practice has layered refinements on the basic rule.
Cost-plus regulation, where the firm recovers audited costs plus an allowed return, is its administrative cousin, while price-cap regulation sets a ceiling and lets the firm keep efficiency gains. Each wrestles with the same incentive problem, namely why economise if costs are always covered, and that weakness is the rule's known flaw because firms may pad costs, gold-plate investments or simply relax while regulators answer with audits, benchmarking and periodic reviews.
The rule's history explains its persistence. Regulators needed a standard that courts would accept as neither confiscating the utility's property nor abandoning consumers, and covering cost including a fair return fit that constitutional balance, so rate cases built around it became the routine theatre of utility regulation for most of a century.
The concept also reaches beyond utilities, since airport charges, port dues and network access fees are set through descendants of the same logic, negotiated with regulators rather than discovered in a market. For managers in regulated industries, the rule defines the business model, because profits come from the allowed return on the rate base rather than margin expansion, while for managers elsewhere it explains why utility prices move through formal hearings rather than market competition.
Energy transition pressures are testing the framework again, since a price set at average cost may not cover fixed network costs spread over fewer units sold when demand stops growing. Investors in regulated utilities learn to read rate-case calendars the way others read earnings seasons, since allowed returns are set there.
In practice
Real-world examples.
Example
A public electricity provider operating the only transmission network in a region charges a regulated tariff equal to average cost instead of the higher monopoly price. Households pay less, and the firm covers its costs including an allowed return. It does not earn the excess profit an unregulated monopoly would.
Example
A regulator reviewing a railway rejects a marginal-cost fare because it would not cover the line's heavy fixed costs of track and signalling. It sets fares at average cost instead. The railway stays solvent without a permanent government subsidy.
Example
A city reviews its bus operator's fares under cost-plus regulation, the administrative form of average cost pricing. The operator submits audited costs, and the council allows fares that cover them plus a modest return. Councillors also ask for efficiency benchmarks, because the arrangement gives the operator little reason to cut costs on its own.
Formula
Calculation
Regulated price P = average total cost (ATC) at the quantity where the ATC curve crosses the demand curve. Economic profit at that point is zero, because price equals average cost.
Worked example. A water utility has fixed network costs, including a fair return on capital, of $4,500,000 a year and variable costs of $2 per unit. At 1,000,000 units a year, total cost is $4,500,000 + (1,000,000 x $2) = $6,500,000, so average cost is $6,500,000 / 1,000,000 = $6.50 per unit. Setting the price at $6.50 gives revenue of 1,000,000 x $6.50 = $6,500,000, which exactly equals total cost.
Pricing at marginal cost instead would mean a price of $2 per unit and revenue of $2,000,000 at the same output. That leaves a loss of $6,500,000 - $2,000,000 = $4,500,000, equal to the fixed costs, which would need a permanent subsidy.Case study
Seen in the real world.
This is a fictional example. Clearwater Valley Water, an invented utility, has a regulated asset base of $100,000,000 and an allowed return of 7%, which is $7,000,000 a year. With audited operating costs of $23,000,000 and 12,000,000 units sold, its revenue requirement is $30,000,000, so the regulator sets the tariff at $30,000,000 / 12,000,000 = $2.50 per unit.
A year later, audited operating costs rise by $600,000 to $23,600,000. The utility files for a review, arguing that the current price no longer covers its audited average cost. The regulator checks the figures, allows the revenue requirement to rise to $30,600,000 and approves a tariff of $2.55 per unit, while asking for a benchmarking study so that higher costs are not simply passed on to customers.
Watch out
Common mistakes.
- Assuming average cost pricing achieves ideal efficiency. It improves on monopoly but produces less than the marginal-cost ideal, by design.
- Ignoring the incentive problem. When all costs are recoverable, firms may overinvest or overspend, so oversight is part of the system.
- Confusing average cost with marginal cost. In declining-cost industries the two diverge, and choosing the wrong one bankrupts the provider.
Questions
People also ask.
Why not force the monopoly to price at marginal cost?
In natural monopolies average cost exceeds marginal cost, so marginal-cost pricing runs at a loss and requires permanent subsidy.
What profit does a firm earn under the rule?
A normal profit: revenue covers all costs including a fair return on capital, but no excess economic profit.
What is the main criticism of the rule?
It weakens cost discipline, since higher costs justify higher prices, prompting variants like price-cap regulation.
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