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

The Lerner Index measures the share of your selling price that is not eaten by cost. It has been the economist's measure of pricing power for the better part of a century, and it is worth knowing by name because it is the formal version of something this lesson uses constantly.

A pure commodity sells right at its marginal cost. Price equals cost, so the index is 0, and there is no pricing power at all. Every unit of price is consumed by the cost of producing it.

A seller with no substitutes can hold price far above cost. As cost shrinks against price the index approaches 1, and the pricing power is close to total.

Real brands sit between the two. A leading brand with genuine equity in a category with credible alternatives runs somewhere around 0.45 to 0.60. The same category's private‑label entry tier runs 0.05 to 0.20. The gap between those two numbers is what brand investment, distinctive packaging and promotional discipline have built over years, and it is exactly what the rest of this lesson is about protecting.

Why this card sits in this lesson. The two‑numbers card asks what your gross margin can afford to lose and calls the answer your limit. That limit is one divided by your Lerner Index. They are the same quantity said two ways, and knowing the formal name is useful because it connects what you are doing here to the wider pricing literature and to Lesson 8, where the same identity turns up again as the condition for an optimal price.

The link to price sensitivity, which is the part worth memorising. At the profit‑maximising price, the Lerner Index equals one divided by the size of your price sensitivity.

A Lerner Index of 0.40 implies a price sensitivity of 2.5 at the optimum. Read it the other way and it becomes a working test: if your Lerner Index is larger than one divided by your price sensitivity, you are priced above the optimum. If it is smaller, you have room you have not taken.

The textbook version.

Where:

• P = the net price per unit you actually realise, after on‑invoice trade terms have come off
• MC = the marginal cost of producing and supplying one more unit

The version you can compute this afternoon. Marginal cost is a clean idea and an awkward number to get out of a real ledger, so most teams compute the Lerner Index off the gross margin instead:

Where:

• COGS = cost of goods sold per unit, the cost to make and move the unit
• P = the same net realised price

That is your gross margin, expressed as a fraction instead of a percentage. So:

Worked example, a biscuit hero pack.

• Net price realised per unit: $2.35
• Cost of goods sold per unit: $1.25
• Contribution per unit: $1.10
• Lerner Index: 1.10 / 2.35 = 0.468
• Your limit: 1 / 0.468 = 2.14

Which is exactly the number the two‑numbers card arrives at from the other direction.

Three notes on the arithmetic, and the third is the one people get wrong.

One. The index is dimensionless and sits between 0 and 1, which makes it a clean way to compare a $1.20 pack against an $8.00 one.

Two. Fixed manufacturing overhead and brand marketing money are not in it. The Lerner Index is about the economics of one more unit, which is why a period cost has no business in it. That is the same rule the two‑costs card sets out.

Three, and this is the caveat to carry with you. The textbook marginal cost would also include the variable cost of distributing the unit, which sits below the gross profit line as cost to serve. Using cost of goods sold gives you a slightly higher Lerner Index than the strict version, so your limit reads slightly more generous than it truly is. That is fine as long as you know it. If you want the conservative number, add variable distribution to the cost side and recompute. On most FMCG packs it moves the index by a few hundredths.

Two biscuit packs sit next to each other at $2.35.

CrunchField is the category leader. Cost of goods sold is $1.25 a unit, so contribution is $1.10 and the Lerner Index is 0.47. Its limit is about 2.14, and with a price sensitivity range of 1.55 to 1.9 it has room.

A mid‑tier challenger cannot match CrunchField's scale on ingredients, on production runs or on distribution efficiency. Its cost of goods sold is $1.65, so contribution is $0.70 and its Lerner Index is 0.30. Its limit is about 3.3.

Read the limits and the first conclusion looks backwards. The challenger's limit is far higher, which by the arithmetic of the two‑numbers card means it can afford to lose more volume on a price rise. That is genuinely true and it is the thin‑margin effect from that card.

Now read the second number and the picture completes. The challenger is also a weaker brand, so its price sensitivity is not 1.55 to 1.9. It sits nearer 2.35 to 2.9. It still clears its limit of 3.3, so a price rise pays for it too, and it pays on a much smaller contribution per unit.

Where the difference actually bites is what each brand can fund. CrunchField has $1.10 per pack to cover overheads, brand investment and operating profit. The challenger has $0.70. If CrunchField spends 5 percent of its net sales on brand support, that is about 12 cents a pack out of $1.10. For the challenger to match that same 12 cents it comes out of 70 cents, which is more than a sixth of everything it earns per unit.

That is what brand power compounding looks like as arithmetic. Same shelf price, same shelf, same shopper. One brand can outspend the other every year without noticing, and the other has to choose each year between supporting the brand and reporting a profit. Over a decade that choice, made annually, is the whole difference between the two engines, and it is the choice the rest of this lesson is about.

What good looks like in mainstream FMCG.

Strong national brand, 0.45 to 0.60. Pricing power is real. The brand can absorb a cost increase, fund brand investment at a meaningful share of net sales, and still run promotions without living on them.

Mid‑tier or value brand, 0.25 to 0.40. Some pricing power, with constant pressure toward commodity behaviour. Promotional intensity tends to be high, because the brand cannot earn its way to growth on price alone.

Private‑label entry tier, 0.05 to 0.20. Almost no pricing power, by design. That tier is sold on lowest net cost, and the retailer takes its value through assortment control rather than per‑unit margin.

Three questions to ask whenever the number moves.

Is it moving on the price side or the cost side? A Lerner Index that rose because cost came out is fragile, because the next input‑cost cycle takes it straight back. One that rose because the brand moved up a price tier and held is durable. The index reads the same either way, so find out which side moved before you record it as a gain.

Is it holding across your major retailers? An index that reads well in aggregate and collapses at one account is usually a trade‑spend allocation problem rather than a pricing problem, and it will not be fixed by a list‑price move.

Is it your brand or the whole category? Everybody's index rises when the category passes through cost inflation together. That is not a pricing‑power gain and it will not survive the first competitor who decides to hold.

One trap worth naming. A rising Lerner Index alongside falling volume is a brand harvesting itself. The index looks better every quarter precisely because the price‑sensitive buyers have gone, leaving a smaller and more loyal base. Read it next to penetration, always, and treat a rise in the index with a fall in buyers as a warning rather than a result.