Perfect Price Discrimination

A regular monopolist charges one price to everyone, so marginal revenue falls below price: selling one more unit means discounting all earlier units too. That gap between price and marginal revenue is what chokes off output below the competitive level and creates deadweight loss. Perfect price discrimination breaks that link. If the seller can identify every buyer's maximum willingness to pay and charge each one exactly that, there is no discount spillover. Marginal revenue from each unit equals its own price, so marginal revenue and demand become the same curve.

Because marginal revenue now tracks demand all the way down, the seller keeps producing as long as price exceeds marginal cost, stopping exactly where price equals marginal cost, the same stopping point a competitive market reaches on its own. Total output matches the competitive quantity, so the deadweight loss triangle that shows up under single-price monopoly disappears entirely. What vanishes instead is consumer surplus: every dollar a buyer would have kept gets charged away, so the entire area between demand and marginal cost becomes producer profit rather than split between buyer and seller.

This is the sharp contrast to sit next to single-price monopoly from earlier in the unit: same market, same cost structure, but pricing strategy alone decides whether output is efficient or restricted. It also sets up oligopoly behavior next, where firms without perfect information about each buyer rely on strategic guessing instead of mind-reading pricing.