One customer at 27% is half your risk
Ten grocery market shares, and the concentration maths every board pack should run and almost none does. The largest player contributes 51% of the entire concentration score — because these measures square the leader.
- Source
- Kantar Worldpanel grocery market shares, Great Britain
- Period
- 12-week period reported August 2026
- Published
- August 14, 2026
- Built with
- Databoat
50.70%
of the entire market concentration score comes from one retailer — because concentration squares the leader, a business twice the size of the next contributes four times the risk
Tesco
- Ocado0.22%
- Co-op1.03%
- M&S1.14%
- Waitrose1.32%
- Lidl4.46%
- Morrisons5.76%
- Aldi7.08%
- Asda12.77%
- Sainsbury's15.51%
- Tesco50.70%
Area is share of take-home grocery till roll, percent. Ten named retailers, 97.8% of the market.
The eye reads area, and area is roughly what intuition tracks. The leader looks about twice the size of the runner-up, and it is — 27.3% against 15.1%. Hold that impression for the next figure, because the maths of risk does not agree with it.
The residual 2.2% held by independents and symbol groups is not shown.
Basis — what this measures
- Sources
- Kantar Worldpanel take-home grocery market shares for Great Britain, as reported in August 2026.
- Period
- A single 12-week reporting period. Kantar reports on a rolling 12-week basis, so this is a snapshot rather than a full year.
- Grain
- One row per named retailer. Share is of total take-home grocery till roll.
- Excludes
- Independents, symbol groups and smaller chains, which together hold the residual 2.2% and are not broken out. Online-only and convenience formats sit inside their parent retailer where the parent is named.
Movement — why the number is what it is
Horizontal: market share, percent. Vertical: that share squared — the retailer’s contribution to the Herfindahl index.
Hover a point
Concentration measures square each share, so the curve is steep at the top. Tesco is 1.8× Sainsbury’s in size and 3.3× in contributed concentration. Doubling in size quadruples your weight in the risk calculation, which is exactly why a single large customer matters more than a headcount of small ones suggests.
Each retailer’s squared share as a percentage of the total index. Sums to 100%.
- Tesco50.70%
- Sainsbury's15.51%
- Asda12.77%
- Aldi7.08%
- Morrisons5.76%
- Lidl4.46%
- Waitrose1.32%
- M&S1.14%
- Co-op1.03%
- Ocado0.22%
One retailer carries 50.7% of the entire concentration score. The bottom four together carry 3.7%. If you were assessing exposure rather than size, nine of these ten names would barely register.
Market share, percent, ranked.
- Tesco27.30%
- Sainsbury's15.10%
- Asda13.70%
- Aldi10.20%
- Morrisons9.20%
- Lidl8.10%
- Waitrose4.40%
- M&S4.10%
- Co-op3.90%
- Ocado1.80%
The familiar view, and the one that leads every trade headline. It is also the one that understates how lopsided the exposure is.
Each retailer as a percentage of the leader’s share.
Only one competitor reaches even 55% of the leader. The distribution has a long, thin tail — which is the shape that produces a high concentration reading even when no single share looks alarming.
Ties — the numbers reconcile
- 2.2% unallocated
Named retailers account for very nearly the whole market
Σ share = 97.8% of 100% - Exact
The Herfindahl index is the sum of squared shares
Σ share² = 1,469.90 - Exact
Contributions to concentration sum to the whole
Σ hhiShare = 100% - Unconcentrated, narrowly
Index sits below the conventional moderate-concentration threshold
HHI 1,470 against the 1,500 threshold
Method
Ten published market shares. Databoat derived four columns from the one: each retailer's contribution to the Herfindahl index, that contribution as a share of the whole, and each retailer's size relative to the leader in two forms.
The Herfindahl-Hirschman Index is the sum of squared shares — the standard concentration measure used by competition authorities on both sides of the Atlantic. Below 1,500 is conventionally read as unconcentrated, 1,500 to 2,500 as moderately concentrated, above 2,500 as concentrated. This market scores 1,470, which places it just inside unconcentrated — a result most people would not guess from a market where one player holds more than a quarter.
Why this belongs in a client's board pack
Swap "retailer" for "customer" and this is the exposure analysis almost no small business runs.
The squaring is the part worth internalising. A customer twice the size of the next one does not carry twice the risk — it carries four times the weight in the concentration calculation, because losing it removes a proportionally larger slice of the base and reshapes everything below it. That is why "our top three are 56% of revenue" is a materially different statement from "we have thirty customers."
The same three numbers — top-1 share, top-3 share, and HHI — take one join between an invoice ledger and a customer list. Most accounting systems can produce the invoice side and no dashboard produces the calculation.
What this doesn't tell you
Market share is not revenue concentration. A grocery market with ten strong players is healthy; a business with ten customers in the same proportions is fragile. The maths is identical and the interpretation is not, which is why the threshold you compare against has to come from context rather than from the index.
This is a single 12-week snapshot rather than a full year, and Kantar's shares move by a few tenths between periods. The residual 2.2% held by independents is not broken out, so the index is very slightly understated — a more fragmented tail would push it down further, not up.
Why we published this
Every derived column states its formula and the reconciliation above shows the squared shares summing to the index exactly, and the contributions summing to 100%. The 2.2% that does not reconcile is stated rather than quietly absorbed.
Kantar Worldpanel grocery market share · Grocery market shares in Great Britain, historic series
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