Pigouvian Tax (Externality) Calculator
Calculate the optimal Pigouvian tax needed to correct a negative externality and restore the socially efficient output level.
Negative Externalities and Market Failure A negative externality occurs when production or consumption imposes costs on third parties not reflected in the market price. Classic examples: factory pollution, carbon emissions, traffic congestion, second-hand smoke. The market overproduces because private costs are lower than social costs.
The Pigouvian Tax Proposed by economist Arthur Pigou in 1920, the optimal tax equals the marginal external cost (MEC) at the socially efficient output. By adding this tax to the private cost, the producer faces the full social cost and reduces output to the efficient level.
Formula Optimal tax t* = Marginal External Cost at Q* Social cost = Private cost + External cost Socially efficient Q* is where Marginal Social Benefit = Marginal Social Cost
Real-World Examples Carbon taxes (e.g. Canada CA$65/tonne CO2), cigarette taxes, congestion charges, plastic bag levies. All attempt to internalize externalities. The challenge is accurately measuring the marginal external cost.