Elena had been running her taco truck in Charlotte for three years when the offer landed. A strip mall two miles from her regular lunch spot had a vacant unit, and the landlord wanted $3,400 a month for it. The unit had sit-down tables, a real kitchen, and a liquor license if she wanted one. Her accountant asked one question before anything else: how many tacos do you need to sell every month just to cover that rent, and can you actually hit that number?
Elena didn't know. Most business owners don't know, because they have never separated their costs into the two categories that actually determine the answer. Today, we will look into those two categories.
The split that changes everything
Every dollar a business spends fits into one of two categories.
- Fixed costs stay the same no matter how much you sell. Rent, salaried wages, insurance premiums, and loan payments show up whether you sell ten tacos or ten thousand.
- Variable costs move with volume. Tortillas, meat, packaging, and hourly labor scale up and down with every order.
The difference sounds simple, and that's precisely why so many owners skip past it. But the split is the single biggest factor in whether growth makes a business more profitable or just busier.
Most expenses aren't purely one or the other. Utilities often carry a fixed base rate plus a variable charge tied to usage. Staffing can work the same way, with a core team on salary and extra hourly help brought on only during busy stretches. Accountants call these semi-variable costs, and separating the fixed piece from the variable piece inside them matters just as much as sorting the obvious line items, since lumping a semi-variable cost entirely into one bucket throws off every calculation built on top of it.
| Cost type |
Behavior |
Truck examples |
Restaurant examples |
| Fixed |
Stays constant regardless of sales volume |
Truck loan payment, permit fees |
Lease, manager salary, insurance |
| Variable |
Rises and falls with each sale |
Food cost, packaging, propane |
Food cost, hourly staff, utensils |
| Semi-variable |
Has a fixed base plus a variable component |
Phone plan with overage fees |
Utilities, seasonal staffing |
The math behind the lease offer
Total cost at any volume follows one equation:
Total cost = Fixed costs + (Variable cost per unit × units sold)
On the truck, Elena's fixed costs ran $1,800 a month, covering her truck loan and permits. Her variable cost per taco, including food and packaging, was $1.10. She sold tacos for $4 each.
The restaurant changed both numbers. Fixed costs jumped to $9,200 a month once rent, a manager's salary, and insurance were added. The variable cost per taco dropped slightly to $0.95 since bulk kitchen equipment lowered her food waste. Same menu, entirely different cost structure underneath it.
Finding the number that matters
To know how many tacos she needed to sell before the restaurant turned a profit, Elena needed to find her break-even point:
Break-even units = Fixed costs ÷ (Price per unit − Variable cost per unit)
For the truck: $1,800 ÷ ($4.00 − $1.10) = 621 tacos a month.
For the restaurant: $9,200 ÷ ($4.00 − $0.95) = 3,016 tacos a month, roughly 100 a day, every day, before she earned a cent of profit.
The truck cleared its fixed costs in the first week of most months. The restaurant needed nearly five times the volume just to break even, and Charlotte's lunch traffic in that strip mall didn't come close to supporting it. The lease looked appealing at first because sit-down pricing is usually higher. But higher fixed costs meant a much steeper hill before any of that higher pricing translated into profit.
Why fixed costs cut both ways
Here's the part that trips owners up. High fixed costs are risky at low volume, but they become an advantage once volume clears the break-even line. This is called operating leverage. Once fixed costs are covered, every additional sale contributes almost pure profit, since variable cost is all that's left to subtract.
The contribution margin shows that clearly:
Contribution margin = Price per unit − Variable cost per unit
On the truck, each taco contributed $2.90 toward covering fixed costs and, eventually, profit. In the restaurant, each taco contributed $3.05. That extra nickel of margin doesn't matter until volume is high enough to cover the much larger fixed base. A food truck with low fixed costs turns a small profit reliably. A restaurant with high fixed costs either fails to cover its base or, once it clears that base, scales profit faster than the truck ever could.
The same split decides hiring and pricing too
The fixed-versus-variable question doesn't only apply to leases. It shapes almost every growth decision a business makes.
Hiring a salaried manager instead of paying hourly shift leads converts a variable cost into a fixed one. That's a bet that sales volume will stay high enough, consistently enough, to justify paying that salary even during slow weeks. Switching a delivery driver from a per-order contractor to a full-time employee does the same thing. It can lower the cost per order at high volume, but it raises the floor a business has to clear every single month regardless of demand.
Pricing works the same way in reverse. A business with mostly variable costs has more room to discount during slow periods, since cutting a sale mostly just gives up a slim contribution margin rather than eating into money already spent. A business with heavy fixed costs has less room to move on price, because a big chunk of every dollar coming in is already spoken for before a single ingredient or hour gets counted.
What Elena learned and you can too
Elena ran the numbers against her actual foot traffic data from three years of catering the same neighborhood and found she was averaging closer to 55 tacos a day, not 100. She turned down the lease and instead bought a second truck, adding roughly $1,600 in new fixed costs against a break-even point she already knew she could clear based on demand in a second part of town.
The lesson wasn't that fixed costs are bad or that variable costs are automatically safer. It's that every growth decision, a new hire, new equipment, or a bigger space quietly moves a business's cost structure in one direction or the other. Knowing which direction to go and doing the break-even math before signing anything are what separate a decision made on excitement from one made on numbers.
Before the next lease, loan, or salaried hire, run the same equation Elena did. The fixed costs will tell you the amount. The variable costs will tell you how big each step up it actually is.
