How to use this calculator
- Enter selling price, marginal cost.
- Choose a display currency, then select Calculate. Results also update after a brief pause while you edit.
- Read the result with the assumptions below. Export details or save a second scenario to compare your choices.
Formula and method
Lerner index=(price−marginal cost)/price.
Assumptions and limitations
Marginal cost is not average total cost; this calculation alone does not establish market power or legal wrongdoing.
Worked example
With selling price = 10, marginal cost = 6, lerner index is approximately 0.4.
What the result means
Measure the gap between selling price and marginal cost as a share of price.
Common questions
How should I interpret lerner index?
Measure the gap between selling price and marginal cost as a share of price.
What should I check before using this result?
Marginal cost is not average total cost; this calculation alone does not establish market power or legal wrongdoing.
Methodology and transparency
Calculation specification reviewed on 2026-10-14. Mathematical implementation is tested against independent reference fixtures. This does not imply review by a licensed financial professional. Read the testing and precision policy.