Allocative Inefficiency of Monopoly
What is Allocative Inefficiency of Monopoly?
A monopoly is allocatively inefficient because it produces where price exceeds marginal cost (P > MC), underproducing relative to the efficient level and creating deadweight loss.
Allocative efficiency requires P = MC, so that the value of the last unit to buyers equals its cost to society. A profit-maximizing monopolist sets MR = MC, and since its MR lies below price, the result is P > MC: the firm restricts output and charges a higher price than a competitive market would. Units that buyers value above their marginal cost go unproduced, and the lost mutually beneficial trades form the deadweight loss triangle. This is the standard welfare critique of monopoly.
Allocative Inefficiency of Monopoly: a worked example
Give a monopolist demand P = 100 - Q and a constant marginal cost of $20. Marginal revenue is MR = 100 - 2Q. Profit-maximizing output solves 100 - 2Q = 20, so Q = 40, and the price comes off demand: P = 100 - 40 = $60. Allocative efficiency instead requires P = MC, so 100 - Q = 20 gives Q = 80 at a price of $20. The monopolist withholds 40 units that buyers value above the $20 they cost to make. Deadweight loss is the triangle between demand and MC across those units: 0.5 × 40 × ($60 - $20) = $800. Look at the last unit actually produced: buyers pay $60 for something costing $20, so price exceeds marginal cost by $40 and the signal to expand is being ignored.
The mistake students make with allocative inefficiency of monopoly
The common slip is shading the deadweight loss up to the marginal revenue curve instead of the demand curve. MR = MC is where the firm made its decision, so MR feels like the relevant boundary. But what society loses on a unit never made is what buyers would have paid for it, and that is read off demand. The triangle's height runs from demand down to MC, stretching from the monopoly quantity out to where demand crosses MC. A second error is equating inefficiency with profit. A monopolist whose fixed costs are large enough to leave zero economic profit still sets MR = MC, still prices above marginal cost, and still loses the same triangle.
Allocative Inefficiency of Monopoly questions
Why is a monopoly allocatively inefficient?
A monopolist maximizes profit where marginal revenue equals marginal cost, and its marginal revenue lies below the price it charges. Setting MR = MC therefore leaves price above marginal cost. Every unit between the monopoly quantity and the quantity where price would equal marginal cost is worth more to buyers than it costs to produce, yet none of those units gets made. Those forgone mutually beneficial trades are the deadweight loss, and they are exactly what allocative inefficiency means.
Is the higher monopoly price itself the deadweight loss?
The extra price is a transfer, not a loss. Buyers who still purchase at the monopoly price hand surplus over to the seller, and that surplus does not disappear from society, it changes hands. Deadweight loss counts only the units never produced, the ones buyers valued above marginal cost that the firm chose not to make. With demand P = 100 - Q and marginal cost of $20, the transfer is the rectangle sitting on the 40 units sold, while the loss is the triangle over the 40 units withheld.
Can a monopoly be productively efficient but allocatively inefficient?
Productive efficiency and allocative efficiency are separate tests, so yes in principle. Productive efficiency means producing at the minimum of average total cost, while allocative efficiency means charging a price equal to marginal cost. A monopolist that happened to pick the output at the bottom of its ATC curve would pass the first test and still fail the second, because MR = MC always leaves price above marginal cost when demand slopes downward. Most textbook diagrams show both failures at once.
Formula / Example
This is the live Monopoly sandbox. Drag the curves, or open the full version.
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