9 July 2026 ยท 6 minute read
Concentration is a number until it is an event
Everyone knows what share of revenue sits with the largest account. Almost nobody has modelled the month it leaves.
Concentration gets reported the way weather gets reported. Largest customer 18 percent, top five 54 percent, noted in the board pack, next item. It sits in the risk section where it has sat for four years, and its presence there is treated as evidence that it is being managed.
It is not being managed. It is being mentioned.
The difference shows up the first time somebody works out what the month looks like, because 18 percent is not a risk in the way that phrase implies. It is a cliff with a date on it that nobody has written down.
The usual picture
What leaves with them
The revenue is the part everyone models, and it is the smallest part of the damage.
Gross margin goes with it, and the cost that was serving that account does not go anywhere for at least two quarters, because the people who serviced it are still employed and the capacity that was built for it is still there. So the margin hit lands immediately and the cost relief arrives slowly, if it arrives at all.
The reference goes too. A large named account is a thing your salespeople put in front of prospects, and the day it stops being a customer it stops being a reference. New business gets harder in the same quarter that you most need new business. That is no coincidence. It is the same event.
And the rest of the base notices. Accounts that sat next to that name in your case studies start asking their own questions, and one of them asks at renewal rather than in a meeting.
An invented example, worked through
Harborline, month three
Harborline Components is invented: a contract manufacturer with 24 customers, 14.24 million dollars of revenue, 31 percent gross margin, 46 people, and a largest customer at 18 percent. Its top five are 54 percent between them.
Take the largest one out in month three and the first thing that happens is not financial. The plant has capacity that was reserved, and the people who ran that account have their week freed up, and neither of those converts into cash for a while.
Then the second order effects arrive. The salesperson who carried that relationship loses their largest reference in the middle of the year. The remaining concentration goes up rather than down, because the same top five are now a larger share of a smaller company. And the supplier who was single sourcing the marine grade billet is now selling less volume, which is a conversation about unit price that goes the wrong way.
None of that appears in the version of this question that gets asked in a board meeting, which is what percentage of revenue is at risk.
- Revenue goes immediately, cost goes slowly
- The reference goes in the same month as the revenue
- Concentration among the survivors gets worse, not better
- Supplier economics move against you at lower volume
Why the number gets treated as a rate
Because everything else in a customer base is a rate. Monthly churn at 2 percent is a perfectly reasonable way to describe two hundred small accounts, where the law of large numbers does the work and a bad month is a small deviation.
Apply the same thinking to twenty four accounts, one of which is 18 percent of you, and it breaks. That account does not churn at a rate. It makes a decision, once, on a date, in a room you are not in, and the outcome is binary.
The honest way to hold it is as a dated event with a probability attached, not as a contribution to an average. That changes what you do about it. You cannot reduce the probability of a rate. You can change what happens in a specific room in a specific month, if you know which month it is.
What to do
Write down the date. For each of your top five, the next date at which they get to make a decision about you. Most companies have this information and have never assembled it into one list, and the list is usually uncomfortable reading because two of the dates are closer together than anyone realised.
Then work out the month, not the percentage. What the profit and loss looks like in the three months after the largest one goes, with the cost base as it is rather than as it would be after a reorganisation you have not planned. If that picture is survivable, concentration is a risk you are carrying deliberately. If it is not, you do not have a concentration risk, you have a single point of failure, and those are managed differently.
The phrase that should be banned from board packs is customer concentration remains elevated. It remains elevated every quarter, it will remain elevated next quarter, and the word remains is doing the work of pretending that a static observation is a form of control.
Run the question instead of arguing about it
Build a twin from whatever record you have, and see the range rather than the one number somebody liked.