Lerner Index Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Lerner Index Calculator turns a familiar business question into a compact set of numbers, so you can see the relationship without building a separate spreadsheet.

What this calculator does

Lerner Index Calculator calculates the Lerner Index from market price and marginal cost to express the price-cost markup as a share of price. That makes the output useful for the specific relationship being measured here, while keeping any unentered business or investment assumptions outside the calculation.

How to use it

Enter Currency, Market price, Marginal cost, and Optional period length (days). Use figures from the same reporting period and the same accounting, workforce, inventory, or campaign definition wherever possible. The currency selector changes display currency only; it does not perform an exchange-rate conversion. Before using the result in a decision, recheck unusually large or negative values against the source data rather than assuming the calculator is correcting an inconsistent input.

How the calculation works

Lerner index = (market price − marginal cost) ÷ market price. A value closer to zero means price is close to marginal cost; a larger positive value represents a wider markup relative to price.

Example

At a market price of $100 and marginal cost of $60, the Lerner index is (100−60)/100 = 0.4.

How to interpret the result

Use the result as a compact description of the inputs you supplied. Compare it with the same metric calculated consistently over time or across alternatives; the number is most useful when its accounting period, denominator, and business definition remain stable.

Limitations and notes

The calculation is only as consistent as its inputs. Accounting policy, attribution rules, period length, one-time items, seasonality, and local reporting conventions can change what should be included in a numerator or denominator. Use the same definitions when comparing periods, and do not treat a simplified ratio as a complete operational diagnosis.