Fixed vs. variable: why your cost structure decides your risk

Two competitors do $1.2m of revenue and $120,000 of profit. One runs a mostly fixed cost base — salaried staff, owned equipment, a long lease. The other subcontracts, rents, and pays commission.

On this year's numbers they look identical. They are not remotely the same business, and a 20% swing in revenue in either direction will make that obvious.

Operating leverage, both ways

A fixed cost does not move when volume does. So once fixed costs are covered, almost all of each additional sale drops to profit — and below that point, almost all of each lost sale comes straight out of it.

The fixed-cost business has higher upside and a real chance of a loss. The variable-cost business gives up profit in good years to buy survivability in bad ones. That is the entire trade, and it should be a deliberate choice rather than an accident of how you happened to grow.

Choose your structure from your volatility

The right answer follows from how predictable your revenue is.

• Stable, contracted revenue. Lean fixed. Subscription bases, long-term contracts and repeat maintenance work can carry fixed costs safely, and the operating leverage is a genuine advantage.
• Lumpy or project revenue. Lean variable. If a quarter can be half of the last one, fixed costs are what turn a slow patch into an emergency.
• Seasonal. Variable through the trough, fixed through the peak, as far as the labour market allows. This is the hardest one to execute and the most valuable to get right.
• Early and unproven. Variable, almost regardless of the cost. You are buying the option to be wrong, and paying a premium per unit for it is a reasonable price.

Most costs are more variable than they feel

Fixed and variable is a spectrum, not a switch, and much of it is a contracting decision rather than a fact of nature. Subcontractors instead of employees. Rented equipment instead of owned. Commission-weighted pay instead of salary. Cloud capacity instead of servers. Shorter leases at a higher rate.

Each converts a fixed cost into a variable one, and each costs more per unit. That premium is the price of flexibility, and it is worth paying exactly when you are uncertain — which is most of the time for a small business.

The direction of the ratchet

The dangerous pattern is drifting toward fixed without deciding to. It happens naturally: a contractor becomes an employee, a rental becomes a purchase, a rolling lease becomes a five-year one. Each step is individually sensible and slightly cheaper per unit.

Then a slow quarter arrives and none of it can be unwound. Reviewing your fixed-to-variable split once a year, alongside the annual plan, is enough to catch it — and the moment to add fixed costs is when revenue has become genuinely predictable, not when you merely hope it will be.