Lerner Index: How Much of Your Shelf Price Is Profit, Not Cost

The Lerner Index, introduced by Abba Lerner in 1934, measures the share of your selling price that is NOT cost. Written L = (P − MC) / P, it captures pricing power in a single number between 0 and 1.

A pure commodity sells right at marginal cost. P = MC, so L = 0. There is no pricing power. Every dollar of price is consumed by marginal cost.

A pure monopoly with no substitutes can hold price arbitrarily above cost. As MC approaches zero relative to P, L approaches 1. The pricing power is total.

Real CPG brands sit between these extremes. A leading brand with strong equity in a category with credible alternatives might run a Lerner Index of 0.45 to 0.55. The same category's private-label entry tier might run at 0.05 to 0.15. The gap between those two numbers is the pricing power that brand investment, distinctive packaging, and promotional discipline have built over many years.

Cross-lesson connection. The Lerner Index is the structural backstop behind Pricing Lesson 1 (elasticity). Brands with low Lerner Index live close to commodity behaviour and respond to price moves with high own-price elasticity (-2.5 to -3.5). Brands with high Lerner Index can absorb a 5 to 10 percent price increase with a much smaller volume impact (own-price elasticity often -1.0 to -1.5). The two measures look at the same underlying truth from different angles.

Definitions for an FMCG context:

P = Net selling price per unit (what the retailer pays the manufacturer, after on-invoice trade terms)
MC = Marginal cost per unit (variable cost of one more unit produced and shipped: COGS plus variable distribution plus variable trade investment per unit)

Worked example for a biscuit hero SKU:
- Net selling price per unit: $2.40
- COGS per unit: $0.95
- Variable distribution: $0.18
- On-invoice trade allowance per unit: $0.32

Marginal cost = $0.95 + $0.18 + $0.32 = $1.45
Lerner Index = ($2.40 − $1.45) / $2.40 = $0.95 / $2.40 = 0.40

Forty cents of every dollar this brand earns at shelf is contribution margin available to absorb fixed costs, fund brand investment, and drop to operating profit.

Three notes on the math:
1. The Lerner Index uses MARGINAL cost, not full unit cost. Fixed manufacturing overhead and brand-marketing dollars are not in the denominator. The Lerner Index measures pricing-power on incremental volume.
2. The Lerner Index is dimensionless and bounded between 0 and 1, which makes it a clean comparison metric across SKUs of very different absolute price.
3. The relationship to elasticity: at the optimal price, the Lerner Index equals the absolute reciprocal of own-price elasticity. L = 1 / |ε|. A Lerner Index of 0.40 implies own-price elasticity of -2.5 at the optimum.

Consider two biscuit SKUs side by side at $2.40 per pack.

Brand A is the category leader. Marginal cost is $1.45 per unit. Lerner Index = 0.40. The brand can fund advertising at 5 percent of net revenue, run quarterly innovation, and still deliver 15 percent operating profit.

Brand B is a mid-tier challenger. Marginal cost is $1.80 per unit because the manufacturer cannot match A's scale on COGS, distribution efficiency, or trade leverage. Lerner Index = 0.25. The brand has 38 cents less per pack to spend on advertising, innovation, or operating profit. To match A's marketing investment in absolute dollars, B has to spend 12 percent of net revenue on advertising. To deliver any operating profit at all, B must run lean on innovation and accept slower growth.

The two brands look identical at shelf. Same price, same pack, same category. The Lerner Index reveals the structural reason why A can outspend B every year and B has to chase share through promo depth that erodes its already thin pricing power.

This is what brand power compounding means in numbers. The same shelf price masks a very different commercial engine on each side.

What good looks like in mainstream CPG:

Strong national brand: Lerner Index 0.45 to 0.60. Pricing power is real. The brand can absorb a price increase, fund advertising at a meaningful share of net revenue, and still run promotional events.

Mid-tier or value brand: Lerner Index 0.25 to 0.40. Some pricing power but commodity drift is a constant pressure. Promo intensity tends to be high because the brand cannot earn its way to growth on price alone.

Private-label entry tier: Lerner Index 0.05 to 0.20. Almost no pricing power by design. The brand is sold on lowest net cost to serve, and the retailer extracts value through assortment leverage rather than per-unit margin.

Three questions to ask when the Lerner Index moves:

1. Is the move coming from numerator (price) or denominator-shrink (cost)? A Lerner Index rise driven by cost-out is fragile. A rise driven by a successful price-tier move is durable.

2. Is the move consistent across all major retailers? A Lerner Index that holds at one retailer and collapses at another is usually a trade-spend allocation problem, not a pricing problem.

3. Is the move category-wide or brand-specific? A Lerner Index rise across the whole category (cost inflation passing through) reads differently from a brand-specific rise (genuine pricing-power gain).