A customer accounts for 25% of annual revenue.
The CFO asks what happens if that customer leaves.
Sales estimates a $5 million revenue problem. Finance applies the company’s 35% gross margin and reports a $1.75 million profit problem.
Both calculations might be wrong.
The customer could be unusually profitable. It might receive substantial discounts. Perhaps the company carries dedicated inventory, leases specialized equipment, or employs people whose workloads would disappear along with the contract.
And then there’s the cash.
Losing a major customer can damage profitability, liquidity, and operating capacity in very different ways.
The correct approach is to build a customer-specific scenario that separates lost revenue, avoidable costs, stranded expenses, working-capital changes, and replacement business.
A percentage-of-revenue calculation is a useful warning. It isn’t a financial forecast.
Start With the Customer’s Actual Economics
Consider a hypothetical company with $20 million in annual revenue.
Its largest customer generates $5 million.
That represents 25% of the business.
Management wants to understand the consequences of losing the account at the beginning of the next fiscal year.
Start with the customer’s revenue and direct economics.
| Customer economics | Annual amount |
|---|---|
| Revenue | $5,000,000 |
| Direct materials and variable production costs | ($2,750,000) |
| Variable freight and commissions | ($250,000) |
| Contribution margin | $2,000,000 |
| Contribution margin percentage | 40% |
The customer generates $2 million in annual contribution.
That amount helps cover fixed operating expenses and profit.
If the customer disappears, the company may avoid the $3 million of variable costs associated with its sales.
But it doesn’t automatically avoid the fixed costs supported by the contribution.
This distinction is where many customer-loss forecasts go wrong.
Calculate the Contribution at Risk
The simplest starting formula is:
Annual contribution at risk = Customer revenue × Customer contribution margin percentage
For this customer:
$5,000,000 × 40% = $2,000,000
The immediate annualized contribution exposure is $2 million, before considering fixed-cost reductions or other changes.
Notice that this is larger than the $1.75 million implied by applying the company’s average 35% gross margin.
Customer-specific economics matter.
A large customer might receive aggressive pricing but require little selling expense.
Another might pay premium prices while demanding expensive customization, dedicated support, and frequent deliveries.
Using a company-wide margin percentage assumes every customer has the same economics.
They rarely do.
Identify Which Costs Actually Disappear
Losing revenue doesn’t mean every associated expense disappears.
Suppose the company has the following annual costs supporting the customer:
| Cost category | Annual cost | Avoidable after customer loss |
|---|---|---|
| Direct materials and variable production | $2,750,000 | $2,750,000 |
| Variable freight and commissions | $250,000 | $250,000 |
| Dedicated customer support team | $300,000 | $180,000 |
| Allocated facility and corporate overhead | $400,000 | $0 |
The $3 million of variable costs disappear with the activity, assuming no minimum commitments, cancellation penalties, or remaining inventory obligations.
The dedicated support team costs $300,000 annually, but management expects to eliminate only $180,000 of that expense.
The remaining $120,000 represents retained capacity or costs that cannot be removed immediately.
The $400,000 of allocated overhead is a different matter.
An accounting allocation doesn’t establish that an expense is avoidable.
The company may still pay the same facility rent, insurance, and corporate salaries after the customer leaves.
Removing allocated overhead from the forecast simply because the revenue disappeared would overstate savings.
The financial impact is therefore:
Lost contribution: $2,000,000
Avoidable dedicated support costs: $180,000
Net annualized operating profit reduction: $1,820,000
This assumes the dedicated support costs are operating expenses below the contribution measure and that there are no additional transition costs or offsets.
The customer represented 25% of revenue, but the annualized operating profit exposure is determined by its contribution and the expenses management can actually remove.
That’s a much more useful number.
Model the Timing, Not Just the Annual Total
The next question is when the customer leaves.
A contract that expires in December creates a different current-year exposure from one terminated in March.
The same applies to costs.
Materials purchases may stop quickly. Employee reductions, lease obligations, and equipment commitments may take longer.
For a monthly scenario model, calculate:
Lost monthly contribution = Lost monthly revenue × Customer contribution margin percentage
Then add back avoidable fixed costs only in the months when those reductions can actually occur.
Assume the customer normally purchases $416,667 per month and exits on April 1.
Nine months of revenue are at risk.
Lost revenue = $5,000,000 × 9 ÷ 12 = $3,750,000
Lost contribution = $3,750,000 × 40% = $1,500,000
Suppose the company can eliminate $15,000 per month of support costs beginning July 1.
Six months of savings equal $90,000.
Current-year operating profit reduction = $1,500,000 − $90,000 = $1,410,000
The first-year impact is $1.41 million.
The annualized impact after support reductions is $1.82 million.
Both numbers are correct for their respective time periods.
Confusing them creates trouble when the following year’s budget arrives.
Add the Cash Flow Consequences
Operating profit and cash flow won’t move together.
The company may still collect receivables from the departing customer after shipments stop.
It may also have inventory that cannot be returned or used elsewhere.
Supplier commitments could require cash payments even when production is canceled.
A proper cash forecast should therefore model the timing of:
- Final customer invoices and collections
- Outstanding receivables and potential credit losses
- Remaining inventory purchases and supplier commitments
- Employee severance or contract termination costs
- Cash savings from reduced production and support expenses
- Replacement-customer receipts and related costs
Consider a simplified example.
At the customer’s departure date, the company has $600,000 of outstanding receivables.
It expects to collect $570,000 and believes $30,000 may be uncollectible.
It also holds $200,000 of customer-specific inventory.
Management expects to recover $80,000 through alternative sales or supplier credits.
The remaining $120,000 may require a write-down.
These items have different effects.
The $30,000 potential credit loss and $120,000 potential inventory write-down affect profitability when recognized under the applicable accounting requirements.
Cash collections, inventory recovery, and supplier payments affect liquidity according to their actual timing.
The forecast must avoid counting the same loss twice.
For example, an inventory write-down is an accounting expense. It isn’t a second cash payment if the inventory was already purchased and paid for.
Similarly, collecting an existing receivable generates cash but doesn’t create new revenue.
A forecast that ignores those distinctions can make a difficult situation look considerably worse—or much better—than it really is.
Don’t Assume Replacement Revenue Arrives Immediately
Management’s first response to losing a large customer is often reassuring.
Sales will replace the business.
Perhaps.
But replacement revenue needs a start date, an expected sales ramp, and its own contribution margin.
Suppose the company expects to replace half the lost annual revenue through several smaller customers.
That would eventually restore $2.5 million in annual sales.
However, the replacement customers may have different pricing, production requirements, and acquisition costs.
Assume the new business produces a 35% contribution margin.
Annual replacement contribution = $2,500,000 × 35% = $875,000
If fully established, that reduces the annualized operating profit exposure:
$1,820,000 − $875,000 = $945,000
The remaining annualized profit gap is $945,000, before any additional costs required to win or serve the replacement customers.
But if the replacement business takes twelve months to reach its target run rate, finance shouldn’t recognize the full $875,000 benefit immediately.
The monthly forecast should reflect the actual expected ramp.
A sales pipeline is evidence of opportunity.
It isn’t revenue until the underlying commercial assumptions support the forecast.
Build Three Customer-Loss Scenarios
A useful scenario model should show management what happens under different responses.
For the same $5 million customer, consider these annualized scenarios.
| Scenario | Customer contribution lost | Fixed-cost savings | Replacement contribution | Net operating profit reduction |
|---|---|---|---|---|
| Customer retained | $0 | $0 | $0 | $0 |
| Customer lost, no replacement | $2,000,000 | $180,000 | $0 | $1,820,000 |
| Customer lost, partial replacement | $2,000,000 | $180,000 | $875,000 | $945,000 |
These figures are annualized steady-state comparisons.
They aren’t predictions of the first twelve months after the customer exits.
For a cash and earnings forecast, the model also needs monthly assumptions about when the account ends, when costs can be reduced, and when replacement sales begin.
Management should be able to change those assumptions without rebuilding the entire spreadsheet.
That is the practical value of scenario modeling.
Test the Assumptions That Could Change the Decision
Not every input deserves equal attention.
For a concentrated customer, the most consequential assumptions are usually the customer’s contribution margin, timing of departure, avoidable fixed costs, and replacement-sales ramp.
There may also be significant contractual obligations or credit exposure.
Finance should identify which assumptions are supported by evidence and which depend on management judgment.
For example, if the company believes it can eliminate $180,000 in annual support costs, someone needs to confirm how.
Will positions be eliminated? Can employees be reassigned to revenue-generating work? Are there severance costs?
If replacement revenue depends on winning three new customers, what supports those opportunities and their expected timing?
A scenario becomes useful when it exposes the decisions management must make.
Otherwise, it’s just a spreadsheet containing three different guesses.
When Should a CFO Act Before the Customer Leaves?
A company doesn’t need to wait for a cancellation notice to evaluate customer concentration.
Warning signs may include declining order volumes, repeated contract extensions, increased pricing pressure, deteriorating payment behavior, or a customer reducing its own operations.
None of these signals guarantees the relationship will end.
They do justify examining the exposure.
A CFO can use the model to answer practical questions:
How much operating profit is at risk?
How long can the company maintain its current cost structure if the account disappears?
Which expenses can be reduced without damaging the remaining business?
Would retaining the customer at a lower price produce a better result than losing it?
And how much cash would the company need during the transition?
That last question can be particularly important when the customer represents a large portion of both revenue and receivables.
A business may remain profitable on paper while experiencing a serious liquidity problem.
Know When a Retention Discount Makes Financial Sense
Suppose the customer threatens to leave unless the company reduces prices by 8%.
On $5 million of annual revenue, the requested discount equals $400,000.
Assuming volumes and variable costs remain unchanged, the customer’s annual contribution would fall from $2 million to $1.6 million.
Management now has a commercial decision.
Retaining the customer at the reduced price could preserve $1.6 million of annual contribution.
Losing the customer without replacement would remove $2 million of contribution, partially offset by avoidable support costs.
That comparison suggests a discount could be economically attractive.
But the analysis isn’t finished.
Finance should consider whether the lower price creates precedent for other customers, whether the relationship remains profitable after customer-specific costs, and whether retaining the account prevents the company from pursuing better business.
The company also needs to know whether the discount would actually secure the contract.
A lower price is only valuable if it changes the customer’s decision.
Discounting an account that plans to leave anyway is a remarkably expensive farewell gift.
The Customer Concentration Report Should Lead to a Decision
A useful customer concentration report should show revenue exposure, customer-specific contribution, avoidable costs, contract timing, and the cash implications of losing major accounts.
It should also identify the person responsible for each assumption.
Sales owns the commercial relationship.
Operations validates capacity and cost reductions.
Accounting supports receivables, inventory, and contractual obligations.
FP&A connects those inputs into a financial forecast management can use.
The resulting discussion becomes much more specific than whether 25% customer concentration is too high.
The relevant question is what the company can withstand if that customer changes its purchasing behavior—and what management can do before the situation becomes urgent.
Forecast the Economics, Not Just the Missing Revenue
Losing a major customer can create a substantial financial problem.
But the revenue percentage alone doesn’t measure it.
The real exposure depends on contribution margin, costs that remain after the customer leaves, timing of collections and payments, and the company’s ability to replace profitable business.
A customer-loss scenario should make those assumptions visible and give management time to respond.
If your revenue forecast assumes major customer relationships will continue indefinitely, The Schlott Company’s Forecasting & Planning services can help build a more realistic forecast that connects customer-level risks to earnings and cash flow.