Glossary term
Lerner Index
The Lerner Index is a measure of market power that compares a firm's price with its marginal cost.
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What Is the Lerner Index?
The Lerner Index is a measure of market power that compares a firm's price with its marginal cost. It estimates how far price sits above the cost of producing one additional unit.
A higher Lerner Index generally signals more pricing power. A lower index suggests the firm is pricing closer to marginal cost, which is more consistent with strong competition.
Key Takeaways
- The Lerner Index measures the markup of price over marginal cost.
- It is commonly used to discuss monopoly power and market competition.
- A value near zero suggests price is close to marginal cost.
- A higher value suggests more ability to price above marginal cost.
- The index is useful conceptually, but marginal cost can be hard to observe in real companies.
The Formula
The standard Lerner Index formula is:
In this formula, L is the Lerner Index, P is price, and MC is marginal cost.
For example, if a branded software company sells a seat for $100 and the marginal cost to serve that seat is $70, the Lerner Index is 0.30, or 30%. The number points to pricing power, but it does not by itself explain whether that power comes from brand, switching costs, patents, scale, or weak competition.
How to Read the Number
Index level | General interpretation | Possible signal |
|---|---|---|
Near 0 | Price is close to marginal cost. | Competition may be strong or pricing power limited. |
Moderate | Price exceeds marginal cost by a visible margin. | The firm may have some differentiation or market power. |
High | Price is far above marginal cost. | The firm may have strong pricing power, barriers to entry, or weak competition. |
What the Index Reveals
The Lerner Index helps explain why some firms earn higher margins than others. A company with strong brand power, patents, network effects, switching costs, limited competition, or regulatory protection may be able to price well above marginal cost. A commodity producer in a competitive market usually has less room to do that.
The concept connects market structure with margins. A high margin is more durable when it is supported by real pricing power. It is more fragile when it depends on temporary scarcity, accounting classification, or unusually low input costs.
Where It Can Mislead
The index is cleaner in theory than in practice. Marginal cost is not always observable from public financial statements. Reported gross margins, operating margins, and unit economics can be rough proxies, but they are not the same as marginal cost.
The index also does not explain why pricing power exists or whether it is sustainable. A high markup can attract competitors, regulators, substitutes, or customer backlash. A low markup can still be attractive if the business has scale, recurring demand, or capital-light economics.
The Bottom Line
The Lerner Index measures how much price exceeds marginal cost. It is a useful way to think about pricing power, competition, and margins, but it should be read with industry structure, cost data, and the durability of a firm's competitive position.