Customer Profitability: Cost to Serve Decides the Ranking

What customer profitability is, and the three lines it needs

Customer profitability is the profit left on one customer, or one group of them, after every cost that customer causes. Written as a line it is revenue from the customer, less the cost of what was sold to them, less the cost of serving them, less whatever was given away in discounts off list.

Three of those four lines are usually available and the third is usually not.

Gross margin is not customer profitability and the difference is the third line. Gross margin stops after the cost of goods, which means it stops before every cost that varies with how a customer behaves rather than with what a customer buys. The spread is large enough to reverse a ranking: in the worked book below, cost to serve runs from 9.0 percent of revenue on the largest accounts to 35.6 percent on the smallest, a gap of 26.6 points that no gross margin line shows.

That is why this analysis exists as a piece of work rather than as a report you pull. Somebody has to decide which overhead lines are caused by customers and on what driver each one is allocated, and those two decisions determine the answer before any arithmetic happens. The rest of this page works one book of business end to end so that both decisions are visible.

Customer profitability ranked two ways on one book of business

Here is a distributor with three segments. Every figure below is invented for the worked example, and every line is computed from the two above it.

Work the large segment first. Gross profit per account is 12 percent of $500,000, which is $60,000. Take off $45,000 of cost to serve and $15,000 remains. Across 40 accounts that is $600,000.

Mid: 22 percent of $80,000 is $17,600, less $12,000 leaves $5,600, and across 300 accounts that is $1,680,000.

Small: 34 percent of $9,000 is $3,060, less $3,200 leaves a loss of $140, and across 2,000 accounts that is a loss of $280,000.

Shares below are rounded to whole percentage points.

The middle segment is 39 percent of revenue and 84 percent of profit. That is the finding, and it would be invisible on a revenue report.

Now cumulate the contribution from best segment to worst, which is the shape the analysis is usually drawn as.

Recomputed by hand. 1,680,000 over 2,000,000 is 0.84. Adding the large segment gives 2,280,000, and 2,280,000 over 2,000,000 is 1.14. Adding the small segment brings the total back to 2,000,000, which is 100 percent by definition.

The curve peaks above 100 percent and then falls back, and the height of the peak is the single most useful number in the whole exercise. Here it says the profitable part of the book earns 114 percent of what the company keeps, and the last segment gives 14 points of it away. On a real book with thousands of accounts the peak often sits far higher, and the distance between the peak and 100 is the money on the table.

Put margin and cost to serve on the same base

This is where the analysis goes wrong most often, and the error survives arithmetic that is otherwise correct. Gross margin is a percentage of revenue. Cost to serve arrives as a dollar amount per account. Comparing the two directly compares a ratio to a level, and the comparison means nothing.

Convert cost to serve to the same base before you say anything about it. For the large accounts, $45,000 on $500,000 of revenue is 9.0 percent. For mid, $12,000 on $80,000 is 15.0 percent. For small, $3,200 on $9,000 is 35.6 percent.

Now the subtraction is legitimate, and each result checks against the dollar figures above: $15,000 on $500,000 is 3.0 percent, $5,600 on $80,000 is 7.0 percent, and $140 on $9,000 is 1.56 percent. The small accounts carry the best gross margin in the book and the only negative net margin, and both facts are true on the same denominator.

Bates White prints the discipline behind this on its own example case. "Even if the math is easy, write out your calculations; correcting a wrong answer is easier when you can clearly identify where the calculations went wrong." Writing the base beside every percentage is the version of that advice this case type needs.

Dropping the loss-making segment usually loses money

The obvious recommendation is to exit the small accounts. Test it before you say it, because the test almost always reverses it.

Dropping them loses their gross profit in full: 2,000 accounts times $3,060, which is $6,120,000. It saves only the part of the cost to serve that actually goes away. Warehouse space, route density, systems, and the people who run them do not vanish on the day the accounts do. Assume 60 percent is avoidable inside a year. Total small-account cost to serve is 2,000 times $3,200, which is $6,400,000, and 60 percent of that is $3,840,000.

Net effect: lose $6,120,000 of gross profit, save $3,840,000 of cost, so the company is $2,280,000 worse off. Company contribution goes from $2,000,000 to a loss of $280,000. Exiting the only loss-making segment turned a profitable distributor into an unprofitable one.

Now find the threshold, because that is the number a client can use. The avoidable share would have to cover the lost gross profit, so it needs to reach $6,120,000 over $6,400,000, which is 95.6 percent. Every dollar of cost to serve in that segment would have to disappear, near enough, before the exit pays for itself. That is a demanding condition and it is very rarely met.

The alternative move is arithmetically much easier. Raise small-account prices by 2 percent and, holding volume, the segment gains 2 percent of $18,000,000, which is $360,000 of pure gross profit. The segment goes from a loss of $280,000 to a profit of $80,000. A 2 percent price change did what a full exit could not.

The netting rule, borrowed from a damages case

The single most useful discipline in this case type comes from a published case at a firm that does not do strategy work at all. Bates White's battery case computes an overcharge, and then corrects it.

Its answer to the second question ends this way. "If you assume that, instead, prices should have continued decreasing at a rate of $0.50 a year, then TalkTek paid $3.50 more per battery than it otherwise would have in 2019 and 2020." Then the third question introduces a cost shock, and the answer changes: "overpayment per unit was $1.50 instead of $3.50, since the actual price per battery of $3.50 above the but-for price is offset in part by the costs for 2019 and 2020 being $2.00 above the trend."

Check it: $3.50 minus $2.00 is $1.50. The $2.00 removes 57 percent of the headline figure, because 2.00 over 3.50 is 0.571.

The general rule transfers exactly to customer profitability. A gap measured against one baseline has to be netted against every other move in the same period. A customer whose discount widened by three points in a year when input costs also rose by two points has cost you one point, and quoting three is wrong by a factor of three. Ask what else moved.

What a discount does to customer profitability depends on its base

Bain publishes a case on a fashion retailer with declining revenue, and it turns on exactly this. Its FashionCo case puts two options side by side, both at 20 percent off. Option A is a rewards program, and its published line reads "With the rewards program, customers always receive 20% off". Option B is intermittent sales, modeled as a "20% discount 3 months per year", with the stated assumption that the discount "would increase pre-sale purchase sales by 100% over those 3 months".

Same headline percentage. Different base. One discounts every transaction for the life of the program; the other discounts a quarter of the calendar. The firm recommends Option B, saying it "is projected to generate $50M more than the awards program (Option A)". The two option totals themselves are published as images we could not read, so we do not reproduce them and we do not redo the firm's calculation for it.

One arithmetic observation on the published text alone is available, and it is worth having. The case gives 10 million customers at $100 of annual pre-sale spend each, which is $1,000,000,000 of customer spend. The $50M gap between the two options is therefore 5 percent of the customer base's annual spend. A promotion design choice is worth five percent of the top line, which is the sort of figure that justifies the analysis.

The market comparison that comes before customer profitability

One check belongs at the front, before you open a single cost line. A customer whose spend is flat is not stable. The Census Bureau's advance retail report puts August 2026 retail and food services sales at $773.9 billion, "up 6.0 percent (±0.5 percent) from August 2025". Against that, a customer spending the same as last year has cut its share of your wallet by about 6 percent in real commercial terms.

This matters because the decomposition above will happily explain a profit problem that is really a share problem. If the small accounts were profitable three years ago at the same cost to serve, the question is what changed in price or volume, and no amount of activity-based costing will answer it.

Put a number on the difference it makes. Take the small segment and suppose its 2,000 accounts spent $10,000 each three years ago rather than $9,000 today. At the same 34 percent gross margin, gross profit per account was $3,400 against $3,060 now, so the segment cleared $200 per account against a $3,200 cost to serve instead of losing $140. Across 2,000 accounts that is $400,000 of profit rather than a $280,000 loss, a swing of $680,000, and it came from a 10 percent fall in spend per account with no change to any cost line. Check the direction: 10 percent off $10,000 is $1,000 of revenue, 34 percent of which is $340 of gross profit, and $200 minus $340 is the $140 loss.

That is the reason the market comparison goes first. Had you started from the cost table, you would have recommended renegotiating logistics contracts in a segment whose problem is that its customers are buying less. The cost work is correct and the recommendation is aimed at the wrong variable.

How we score a profitability answer, and whose scale this is

No consulting firm publishes a marking scheme for quantitative work. Bain publishes a full profitability case with no weighting; Bates White publishes model answers with no weighting. The hundred points below are ours, written by us and read out of src/lib/grading/rubrics.ts. They are what our own grader measures on numerical work, and no firm has seen them.

Four things to do with an unprofitable customer

Exit and reprice are the two moves everyone reaches for, and the sections above show one of them failing and the other working. There are four, and the order below is by how much of the relationship they disturb.

1. Reprice. The cheapest move and the one the arithmetic above favors. Two percent on the small segment turns a $280,000 loss into $80,000 of profit, with no change to how anything is done.
2. Recover the cost rather than the price. Charge for what was free. Delivery below a minimum order, expedited shipping, returns handling, extended credit. On the small segment, a $200 delivery minimum charge on half of 2,000 accounts earning it twice a year is 2,000 times 0.5 times 2 times $200, which is $400,000, and that alone clears the loss.
3. Change the service model. Move the segment to a cheaper channel: self-service ordering, scheduled rather than on-demand delivery, a shared account manager rather than a named one. This attacks the cost to serve directly, and the test is the same avoidable-share question as an exit, applied to a line rather than to the whole.
4. Exit. Last, because the test in the section above says it needs 95.6 percent of the cost to serve to be avoidable before it pays. That condition is close to never met inside a year.

Three of the four leave the customer in place. That is the practical conclusion of a customer profitability analysis far more often than a cull is, and it is the opposite of what the phrase firing your customers suggests.

One sequencing rule covers all four. Price and fee moves can be tested on a subset next quarter and reversed. Service-model changes take a year and are hard to undo. Run the reversible ones first, and use what they teach you about elasticity before committing to the ones that are not.

Five customer profitability questions to ask about a segment

1. What is in cost to serve, by line item? Delivery, order handling, returns, support calls, credit terms, discounts off list. Ask which are measured and which are allocated.
2. What share of it is avoidable within a year if the segment goes? This is the number the exit decision turns on, and the case will rarely volunteer it.
3. Is the cost driver the account or the order? Two hundred accounts ordering monthly and two hundred ordering weekly have the same account count, and the weekly group generates more than four times the order volume.
4. How do payment terms and returns differ across segments? Both are real cost and both are usually invisible in a gross margin line.
5. What did this segment look like three years ago? A segment that has always been marginal is a pricing question. A segment that has deteriorated is a volume or mix question.

Question two is the one that separates a recommendation from a slide. Questions three and four are where the number actually hides.

Drilling customer profitability on cost to serve

Take any profitability case and force the decomposition twice: once by segment and once by cost driver. The two rarely agree, and the disagreement is the insight. Then run the exit test on the worst segment, every time, and compute the avoidable share that would be needed rather than the one you assumed.

The habit that pays fastest is putting every percentage on a named base before it leaves your mouth. Margin on revenue. Cost to serve on revenue. Growth on last year. It takes two words and it removes the most common way a correct calculation becomes a wrong recommendation.

Where the prompt is a general profit decline rather than a customer-level question, the equation to start from and a full case worked on it sit on the profitability framework. Where the value of a customer has to be carried over years rather than one, the arithmetic is on customer lifetime value. Where the question is whether volume itself fixes the margin, it moves to scale against profitability, which puts a ceiling on what growth can deliver. Where the segment decision is really an investment decision with a payback attached, return and payback is the frame.

The weights above and the reasoning behind them sit on how an answer is assessed. The math drill reports the four dimensions separately after each attempt and names the first to fix, which is how a Units problem stops reading as carelessness. Every figure here is reproducible from the text, and nothing sits behind a sign-up.