Merchant portfolio concentration: how much of your book is really carrying it

Every ISO owner knows their book has a few big merchants. Fewer know how big, because the residual report is organised by merchant, one row each, and nothing in it says "these twelve rows are half your income". We measure this in the residual books we work with, across processors and across countries. This is what the data shows, why the raw file makes the answer wrong, and how to measure your own.

Three portfolios, three shapes

To make it concrete, here are three portfolios of different sizes, each one a real book for one real month, aggregated per merchant. The figures are rounded and the processors are not named.

One caveat, stated up front. The profit measures differ between processors, so these books are comparable in shape, not to the cent. A single month is a snapshot, not a trend. The point is the method, which you can run on your own book in an hour.

Finding 1: half the merchant list is a rounding error

Share of monthly profit produced by different slices of each merchant list, ranked by profit:

In portfolios A and B, the bottom half of the entire merchant list produced under 6% of the month's profit. In B the top 5% of merchants produced more than half of everything. That is the shape we see most often.

Portfolio C is the interesting one. It is far flatter: the bottom half produces over a quarter of the profit, and the top 10% under a third. It is a smaller book with a much higher median profit per merchant, about $200 against $50 to $80 in the other two, and profit is spread far more evenly across it.

So concentration is not a law of the industry. It is a property of how a particular book was built: what kind of merchants were sold, at what pricing, by whom. C's owner and B's owner run different businesses, even though both would describe themselves as an ISO with a few hundred merchants.

Why it matters. Service effort is usually spread evenly across the merchant list. Every merchant gets the same onboarding, the same support line, the same statement. Profit is not spread evenly. Knowing which half of the list is 5% of the money changes where the support time goes, and which merchants get a call when their volume dips.

Finding 2: three people carry half the book

Where a book carries rep attribution, the same pattern shows up on the people side. Two portfolios with roughly twenty-five reps each:

Three reps out of about twenty-five produce about half the profit. In C, one rep produces nearly a third of it. Notice that C, the flat book on the merchant side, is the concentrated one on the rep side. The two risks are independent, and a book can carry either without the other.

Why it matters. This risk never appears on a residual report, because the report groups by merchant, not by rep. It is also the concentration a portfolio buyer asks about first, and the one most owners cannot answer without building a spreadsheet. If three people leave, half the book goes with them, either because their merchants follow them or because nobody else has the relationship. Knowing who the three are is the start of doing something about it: a retention conversation, a succession plan for the accounts, or simply not being surprised.

Finding 3: the processor's file is nearly half closed accounts

This one changes the other two.

Processor files routinely list closed and pending accounts alongside live ones. In portfolio A's file, the largest of the three, the report listed about 2,200 merchants, and just under half of them, 48% of the rows, were closed or pending. Each one sits in the file with zero volume and zero profit, looking exactly like a live merchant until you read the status column.

Anyone sizing that book by counting rows was wrong by nearly double. And every per-merchant average built by hand from the file was wrong in the same direction: average profit per merchant across the raw file came to about $54, across active merchants only it was about $105. Same book, same month, one column of difference.

Before you measure concentration, or attrition, or anything else per merchant, filter to active accounts. It takes two minutes and it is the step most spreadsheets skip.

How to measure your own book in an hour

1. Take one month's residual reports, every processor. Filter to active merchants using the status column, and match merchants across reports by merchant ID.
2. One row per merchant, total profit for the month. If a merchant appears on several rows or several reports, add them up.
3. Sort by profit, descending. Add a running total as a share of the whole.
4. Read off three numbers: the share held by the top 10% of merchants, the share held by the bottom 50%, and the profit of the merchant at the halfway point. That is your merchant concentration.
5. Add the owning rep to each row, group by rep, and sort. Read off the top rep and the top three. That is your rep concentration.
6. Write the six numbers down with the month. Do it again next quarter. The direction is worth more than the level.

What to do with the answer

• If the book is concentrated (top 10% of merchants over half the profit): those merchants deserve a named owner, a quarterly call, and a rate review before a competitor does one. Watch them for the attrition signals in Merchant attrition warning signs, because losing one of them is worth losing fifty from the bottom half.
• If the book is flat: it is more resilient, and it probably means the office's pricing and merchant selection are consistent. Protect that as it grows.
• If three reps carry half: know it, and act on it before a departure forces you to. Shared accounts, overrides and clear ownership in the agreements are the structural answers; the personal answer is that those three should not learn how important they are from a competitor's offer.
• Either way, stop spreading support evenly. The bottom half of the list still needs service, but it does not need the same service.

Frequently asked questions

How concentrated is a typical merchant portfolio? It varies widely between books. In the concentrated ones we analyse, the bottom half of the merchant list produces under 6% of monthly profit and the top 10% produces half to two thirds. Flatter books exist, with the top 10% producing under a third. Measure your own rather than assuming.

What is a healthy level of merchant concentration? There is no fixed threshold. A flatter book is more resilient to losing any one merchant, and a concentrated book earns more per service hour but carries more risk in its top accounts. The useful questions are whether the concentration is rising, and whether the top accounts have a named owner watching them.

How do I calculate merchant concentration from a residual report? Filter to active merchants, total profit per merchant across all reports for the month, sort descending, and add a running share. The share held by the top 10% and by the bottom 50% are the two figures to track over time.

Why is my average profit per merchant so low? Check whether the average includes closed accounts. Processor files commonly list closed and pending merchants with zero profit. In the example above, excluding them nearly doubled the average, from about $54 to about $105 per merchant.

Does rep concentration matter if agents are on lifetime residuals? Yes. Residual terms affect what happens to the money when a rep leaves, but not the relationships. The merchants a departing rep sold are the ones most likely to be re-solicited, and the ones where nobody else in the office knows the owner.

Can software measure portfolio concentration each month? SplitRun shows the share of the house's profit held by the largest merchants and by the largest processor on the dashboard each month, with the change from a year earlier in percentage points, and reads active merchants rather than raw rows. Agent contribution is on the same dashboard. See the sample agent report.