Fixed Costs, Variable Costs and Why the Split Matters

Short Answer: A variable cost rises and falls with how much you sell: materials, fuel, hourly crew time, card fees. A fixed cost stays roughly the same whatever you sell: insurance, software, rent, loan interest. The split matters because it tells you what each extra dollar of sales leaves you, how hard a slow month hits profit, and how much new revenue a fixed commitment like a hire has to bring in before it pays for itself.

Most owners know their costs by category: payroll, supplies, insurance. Few have sorted them by behavior, which is the question that matters when sales change. Once you know which costs follow sales and which don't, you can predict what next month's profit will do from one number.

What Is a Variable Cost?

A variable cost moves in step with volume. Mow twice as many lawns and you burn roughly twice the fuel. Install twice as many garden beds and you buy twice the plants. If sales stop, variable costs stop too.

What Is a Fixed Cost?

A fixed cost is the same whether you have a record month or a dead one: the insurance premium, the software subscription, the accountant's fee, interest on the truck loan, depreciation on equipment you already own. Fixed costs are sometimes called overhead. They're what you owe for being open.

What About Costs That Are Both?

Some costs sit in between, and they're usually the biggest ones.

• Step costs stay flat until volume crosses a line, then jump. A crew member can handle a certain number of jobs; the next job past that needs another person or another truck.
• Mixed costs have a fixed base plus a variable part, like a phone plan with overage charges or a truck that costs insurance every month and fuel only when it drives.

Labor is the classic in-between cost. Hourly crew sized to the season behaves like a variable cost across a year. Inside a single week, the same crew is fixed: a rained-out Tuesday still has to be paid.

A Worked Example: Sorting a Landscaping Company's Costs

Take a hypothetical landscaping company, Greenline Landscaping: one owner, a crew of four in season plus a two-person winter crew for snow removal and cleanups, two trucks, about $520,000 a year in revenue, most of it earned April through October. Here are its costs, sorted by behavior:

Greenline's variable costs are 64% of revenue. That leaves 36 cents of every sales dollar to cover fixed costs and then become profit. That 36 cents is called the contribution margin: what each dollar of sales contributes after the costs it caused.

Fixed costs run about $6,100 a month on the P&L, every month, including January. Less of that leaves the bank: $20,000 a year is depreciation, and the ads run only April to October, so the cash part is about $3,558 a month in winter and $5,058 in season.

Why Does the Split Matter?

It Tells You What a Slow Year Costs

If Greenline's revenue fell 10%, from $520,000 to $468,000, variable costs would fall with it, but fixed costs wouldn't. Profit drops by the lost contribution:

$52,000 × 36% = $18,720

Profit before owner pay goes from $114,000 to $95,280, a 16% drop from a 10% sales decline. The same math runs in reverse: a 10% better year adds $18,720. The higher your fixed costs are relative to revenue, the more profit swings with every change in sales.

It Tells You What a Hire Has to Bring In

Say Greenline's owner is thinking about a fifth crew member at about $50,000 for the season. Treated as a new fixed commitment, that person has to generate enough work to cover their own pay plus the materials and fuel their jobs use. Materials and fuel run about 25.5% of revenue, so each dollar of new work leaves about 74.5 cents toward the new wage:

$50,000 ÷ 0.745 = about $67,000 of new revenue just to break even on the hire

That's before the owner earns anything extra from it. If the calendar can't absorb $67,000 of additional work, the hire makes the business busier and poorer.

It Tells You Your Break-Even

Once you know fixed costs and contribution margin, you can calculate the revenue where profit is exactly zero. That's the subject of its own article, but the short version for Greenline is $73,200 ÷ 36%, or about $203,000 a year.

How Do I Sort My Own Costs?

Go down last year's expense list and ask one question of each line: if sales had been 20% lower, would this cost have been 20% lower too?

• Yes, roughly: variable.
• No, not at all: fixed.
• Partly, or only after a while: step or mixed. Decide which way it behaves over the period you're planning for. For a one-year plan, seasonal crew is variable. For next week's schedule, it's fixed.

Don't chase precision. Getting the big lines right matters far more than classifying a $30 software add-on.

What to Look For

• Fixed costs as a share of revenue. Greenline's is about 14%. The higher it goes, the harder a slow season hits and the more a good one pays.
• Fixed costs added in good years. A second office, a bigger software plan, a financed truck: each one raises the floor you have to clear every month, including the slow ones.
• Variable costs creeping up as a share of revenue. If materials go from 17% to 19% of revenue, every dollar of sales now leaves less behind, and your break-even moves up.

What a Finance Consultant Would Do Next

A consultant looking at Greenline would focus on the in-between costs. They'd ask how much of the crew cost can flex in a wet month or a slow fall, what a fifth crew member would have to bring in at current prices, and whether any fixed cost could become variable (renting a second trailer by the job instead of buying one). Then they'd run the slow-year case, 10% or 20% down, to see whether the owner's pay survives it.

That analysis is what Occam's Model runs on your own books. It separates the costs tied to each thing you sell from your operating expenses, and lets you test a cost cut or a change in volume against your numbers before you commit. When you need extra help, an expert can review it with you.

Common Questions

Is labor a fixed or variable cost?
It depends on the period and the pay arrangement. Hourly or seasonal crew sized to demand is variable over a year and fixed over a week. Salaried staff are fixed. Owners usually treat salaried office staff as fixed and job crews as variable.

Is rent a fixed cost?
Yes. It's the textbook fixed cost: the same amount whether you sell a lot or nothing.

Are fixed costs bad?
No. Fixed costs are often what makes growth possible, like a truck or a skilled employee. They raise risk in slow periods and raise profit in busy ones. The question is whether your worst realistic month can still cover them.

What is contribution margin?
Revenue minus variable costs, usually shown as a share of revenue. It's what each extra dollar of sales leaves to cover fixed costs and then become profit.