A building materials distributor closes out the month with a perfectly balanced cost spreadsheet: warehouse rent, staff payroll, fleet depreciation—all allocated per unit sold and added to each product’s purchase cost. The same margin is then applied across the board: 28% on everything. It works in the sense that the company does not lose money. But the owner has long noticed that some items sell for half the competition’s price, while others sit on the shelf because they are too expensive for the value they offer. The spreadsheet is right, but the price is wrong—and the problem lies not in the calculation, but in the formula.
The problem starts before the margin: it starts with the cost used to calculate it. When the formula adds fixed and variable costs before applying the margin, the final price becomes rigid in a way the market will not tolerate. And that rigidity is easy to miss because the spreadsheet still adds up and the monthly figures still balance—the only thing becoming increasingly rare is having the right product at the right price.
What Changes When Fixed Costs Enter the Equation
Variable costs arise from producing or purchasing a specific unit: the price paid to the supplier, shipping for that batch, and the commission on that sale. Fixed costs are expenses the company pays regardless of whether it sells one unit or a thousand: rent, administrative payroll, equipment depreciation, and management software.
When the formula uses variable cost plus margin, there is room to adjust the margin: it can be higher on a fast-moving product and lower on another without compromising the coverage of costs already accounted for across the business. When the formula uses total cost—variable cost plus the share of fixed costs allocated to that unit—the margin loses this flexibility. It has to balance the entire equation on its own, covering everything the company spends while still delivering the desired profit. This leaves only one viable path for the price, with very little room to adjust it from one product or customer to another.
The most common result of this constraint is a single margin: the same percentage applied across the entire product line, regardless of how much each item is worth to the buyer. This is not a deliberate choice—it is the consequence of a formula that leaves no other option. A margin that never changes no longer conveys any information about the product or the customer; it has become just a fixed number repeated in every row of the spreadsheet.
Why This Limits Value, Not Just Price
A replacement item that is hard to find elsewhere is worth far more to someone who needs it right then and there than the cost of restocking it. A commodity item, available at any store in the area, has its value set by the lowest-priced competitor, with almost no connection to its purchase cost. A total-cost formula that applies the same margin to both ignores this difference by design: the price is based on cost, not on what the product means to the customer.
Pricing literature has a name for this: when cost alone determines the price, leaving no room to account for competition or perceived value, the result tends to be an unrealistic price—too high for what the market is willing to pay, even if it fully covers the company’s cost structure. Customers do not pay for a seller’s inefficiency; they pay what the product is worth to them. A rigid formula cannot capture this difference because it was designed to protect accounting results, not to reflect demand.
The Calculation That Shows the Difference
Take a product with a variable cost of R$ 40—the amount paid to the supplier plus shipping for that batch. When rent, payroll, and depreciation are allocated based on average sales volume, the item carries an additional R$ 15 in allocated fixed costs, bringing its total cost to R$ 55.
Using the total cost formula and a 30% markup on cost:
price = total cost × (1 + markup) = R$ 55 × 1.30 = R$ 71.50
However, this is a fast-moving product in a highly competitive market, and its market price is around R$ 62. At R$ 71.50, the store loses sales every day. Recalculating based solely on variable costs—excluding fixed costs, since they are covered by the normal sales volume—and using a leaner 18% markup, consistent with a narrower contribution margin per unit:
price = variable cost × (1 + markup) = R$ 40 × 1.18 = R$ 47.20
This price can be lowered well below the market price of R$ 62 while still generating a positive contribution margin per unit. The difference between R$ 71.50 and a competitive price of R$ 60 is not due to a calculation error—it comes from adding fixed costs before the markup, which pushed the price to a level the product cannot support on its own.
None of this means selling below variable cost or losing control of fixed costs. They still exist and must be covered by the company’s overall results. The difference is where they enter the equation: in each product’s pricing formula, constraining its individual margin, or in the overall results, allowing each price to reflect what that specific item is worth.
How to Spot the Symptom in Your Own Spreadsheet
Some signs indicate that total cost is holding back pricing before you even review the numbers one by one:
- the same margin is applied to nearly every product, with only a few manual exceptions;
- fast-moving, highly competitive products are priced above market rates;
- exclusive or niche products are priced below what customers would be willing to pay;
- changing the sales mix or production volume changes the fixed cost allocated per unit, causing the price to shift automatically, without any commercial decision behind it.
Any of these signs points to the same root cause: the formula is letting fixed costs determine each product’s price instead of leaving that decision to someone who understands the market for that item.
The adjustment that fixes it without losing control
The answer isn't to stop calculating fixed costs—it's to change where they factor into the decision. Treat fixed costs as something the entire operation needs to cover, based on overall results, the break-even point, and total sales volume. Use variable costs as the basis for each individual price, with the contribution margin reflecting competition and value for each product.
Keeping the two calculations separate requires a costing structure that clearly distinguishes fixed costs from variable costs, along with a selling price calculator that applies the margin to the right cost base in each case—not to a generic total cost that treats every item the same way. Without this separation, every change in product mix or sales volume alters the allocated fixed cost and shifts the prices of products whose market positioning should remain unchanged.
It is also worth reviewing the concept of contribution margin before changing the formula: it replaces the margin on total cost when fixed costs are removed from each product’s calculation and managed based on the company’s aggregate results.
What undermines the margin is not the size of the fixed cost, but where it enters the formula. A company may keep tight control over every cent spent on rent and depreciation and still misprice every fast-moving product—because it insists on letting fixed costs answer, item by item, a question only the market can answer.
