Fixed vs Variable Costs: What's the Difference for Contractors?

A fixed cost stays about the same over a short period even when your job count changes, while a variable cost rises and falls with the work. In a trades or home-services business, shop rent is fixed and paint is variable. A truck is both, and that third group decides what one more job leaves you.

What is a fixed cost?

A fixed cost holds steady over a month or a quarter no matter how many jobs you run. Shop rent, base software subscriptions, salaried office and supervisor pay, some insurance premiums. In the example below, a painting company carries $8,000 of fixed costs a month, and that bill arrives whether you run eight jobs or eighteen.

What is a variable cost?

A variable cost rises and falls with the work. Materials, hourly field labor on the job, piece-rate subcontract work, fuel, dump fees — the costs that exist only because a job exists. On the extra $2,000 job below, added labor, materials, and travel come to $1,200. Turn the job down and you never spend it.

Do not drop the whole payroll line in the variable column. Salaried office and supervisor pay is fixed for the month; only the crew hours a job adds are variable. Calling it all variable makes fixed costs look small, break-even look low, and a discount look safe, and none of that is true.

What's the difference?

Fixed costs are owed whether or not you sell a job. Variable costs exist only because you sold one. The painting company's $8,000 of monthly fixed costs lands either way; the $1,200 an extra job adds does not. A third group matters: mixed costs carry both behaviors in one line, and step costs stay flat and then jump.

A truck has a fixed lease payment and a fuel bill that moves with the miles. A supervisor is fixed until a second crew forces a second one. Sorting costs by behavior is a separate pass from tagging them to jobs, which is direct vs indirect costs.

What does one more job cost?

One more job costs only the money the job adds. A fictional painting company takes an extra job that pays $2,000, and the extra labor, materials, and travel come to $1,200, so the job leaves $800. That $800 is contribution: job price minus the variable costs of that job.

Divide monthly fixed costs by contribution per job. At $8,000 of monthly fixed costs and $800 a job, that is 10 jobs to cover the fixed column, with profit starting on job 11. Cutting fixed costs works as well as selling more, so keep a real list of business overhead costs.

That $1,200 is not fixed either. Once the crew is full, the same job can bring overtime, a rented truck, or a better job bumped to next month, so more volume is not automatically the fix for a margin problem. Check your real weekly room first: capacity planning.

Sorting your own costs takes about an hour with last month's expenses open. Work down from the largest lines, split anything mixed, handle payroll name by name, then total the fixed column and divide. The output is one number you can price against.

1. 1
   Rank one normal month

   Pull every expense line from your accounting file and sort by amount.

2. 2
   Label the top 20 lines

   Mark each one fixed, variable, or mixed, and ignore the tail.

3. 3
   Split the mixed lines and payroll

   The truck becomes lease plus fuel. Salaried pay is fixed; job-created hours are variable.

4. 4
   Divide, then price the next quote

   Fixed total ÷ contribution on a typical job = jobs before profit starts.

Three ways to handle this

There are three practical ways to do this: use a spreadsheet, ask your accountant or bookkeeper, or connect your tools so Barry AI can group fixed, variable, and mixed costs, estimate a job's contribution, and show its assumptions.

Barry, review my connected expenses and group likely fixed, variable, and mixed costs. Use recent similar jobs to estimate what my next booked job will contribute after added costs. Show assumptions.

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