What Is Contribution Margin?

By BRIX Editorial Team · Updated October 12, 2026

Contribution margin is the money a sale leaves after subtracting every cost that varies with that sale, before fixed costs. Contribution margin = Price − Variable costs; the ratio divides that by price. A $14,000 roof with $11,140 of materials, crew pay, commission and fees contributes $2,860, a 20.4% contribution margin ratio.

Key takeaways

Contribution margin = Price − all variable costs. Contribution margin ratio = Contribution margin ÷ Price.
It differs from gross margin by including variable costs that sit below the gross profit line, like sales commissions, card and financing fees, and per-job fuel.
It's the number to use for break-even math, discounts, promotions and deciding whether to take a low-priced job.
Discounts come straight out of contribution margin, so a 10% price cut can wipe out far more than 10% of a job's contribution.
A job with positive contribution helps pay fixed costs even if it doesn't show a profit on its own; a negative one makes things worse with every sale.

How does contribution margin work?

Contribution margin splits your costs into two piles. Variable costs rise and fall with each job: materials, crew pay that's tied to the work, commissions, card fees. Fixed costs stay the same whether you run ten jobs or a hundred: rent, office staff, insurance, software. Contribution margin is what each job "contributes" toward fixed costs, and once they're covered, toward profit.

Contribution margin formulas

Contribution margin = Price − Variable costs   |   Contribution margin ratio = Contribution margin ÷ Price

Price: what the customer pays for the job, before sales tax
Variable costs: every cost that exists only because this job happened and grows with its size or count
Ratio: the share of each sales dollar left to cover fixed costs and profit

What's the difference between contribution margin and gross margin?

Gross margin subtracts cost of goods sold, which follows accounting rules about what's a direct job cost. Contribution margin subtracts every variable cost, wherever it sits on the profit and loss statement, and leaves out fixed costs even if they're in COGS. The two often look similar, but they answer different questions.

Which costs each margin subtracts
Cost	Gross margin	Contribution margin
Materials and parts	Subtracted	Subtracted
Crew pay tied to the job (per job, per square, piece rate)	Subtracted	Subtracted
Hourly techs paid a full week regardless of volume	Subtracted	Often treated as fixed in the short run
Subcontractors, permits, dumpsters	Subtracted	Subtracted
Sales commissions and tech spiffs	Usually not (they sit in overhead or selling expense)	Subtracted
Card processing and customer financing fees	Usually not	Subtracted
Fuel and mileage per job	Usually not	Subtracted if you track it per job
Rent, office staff, insurance, software	Not subtracted	Not subtracted (fixed)

Where commissions and fees land depends on your chart of accounts. The point is that contribution margin catches them all.

Use gross margin to read your profit and loss statement and set prices against direct costs. Use contribution margin for decisions about volume: break-even, discounts, promotions and whether a low-priced job is worth taking.

How does a discount affect contribution margin?

A discount comes almost entirely out of contribution margin, because materials and crew pay don't shrink when the price does. That's why a small percentage off the price can cut a job's contribution nearly in half, and why you need far more jobs to make up for it.

Before discounting, offer a smaller scope instead. Good-better-best pricing lets a price-sensitive customer choose a lower option without you cutting the margin on the same work.

Is a loss-leader promotion worth it?

A promotion is worth it only if the follow-on work it brings in adds more contribution than the promotion gives away. Work out the contribution on the promo itself, then estimate how many promo customers buy something else.

Contribution margin by trade

The variable costs that separate contribution margin from gross margin are different in each trade. These are the ones worth tracking per job.

Variable costs that gross margin often misses, by trade
Trade	Variable costs to include	Decision it helps with
HVAC	Comfort advisor commissions, tech spiffs, customer financing fees on replacements	Whether to offer 0% financing promos and how much to discount a system
Plumbing	Tech commission on sold work, card fees, after-hours premium pay	Whether to drop the trip fee or after-hours charge
Electrical	Permit and inspection fees per job, card fees	Minimum charge for small service calls
Roofing	Sales rep commission, financing fees, per-square crew pay	How far a rep can negotiate on price
Landscaping	Fuel and dump fees per visit, per-visit crew pay	Whether to add a far-away account to a route
Cleaning	Per-visit cleaner pay, supplies, drive time between homes	Whether to accept one-off deep cleans at a discount

Common contribution margin mistakes

Leaving out commissions and fees. They're invisible in gross margin but come off every sale.
Calling fixed costs variable. If a cost doesn't go away when the job doesn't happen, it's fixed. Spreading rent per job hides that.
Judging a promotion by revenue. A busy month of $79 tune-ups can bring in a lot of revenue and almost no contribution.
Discounting without the math. Calculate how many extra jobs a discount needs before you offer it.
Using one ratio for every job type. Repairs, installs and maintenance visits carry very different contribution margins. Track them separately with job costing.

Frequently asked questions

How do you calculate contribution margin?

Subtract every variable cost of a sale from its price. For a $14,000 roof with $11,140 of materials, crew pay, dumpster, commission and fees, contribution margin is $2,860. Divide by the price to get the ratio: 20.4%.

What is the difference between contribution margin and gross margin?

Gross margin subtracts cost of goods sold. Contribution margin subtracts all variable costs, including commissions, card fees and financing costs that usually sit below the gross profit line, and excludes fixed costs. Use gross margin for financial statements and contribution margin for volume and pricing decisions.

What is a good contribution margin ratio?

One that, multiplied by your revenue, covers fixed costs plus the profit you want. If fixed costs are $30,000 a month and you expect $80,000 of revenue, you need at least a 37.5% ratio to break even. There's no universal target because cost structures differ so much between trades.

Can contribution margin be negative?

Yes. If variable costs are higher than the price, every sale loses money before fixed costs are even counted. Deep discounts, underpriced promotions and jobs that run far over the estimated hours are the usual causes.

Is labor a variable cost?

It depends on how you pay. Crew paid per job, per square or by piece rate is variable. Hourly techs paid for a full week no matter what act like a fixed cost in the short run, because you pay them whether or not the job happens. Overtime is variable.

How is contribution margin used in break-even analysis?

Break-even jobs equal fixed costs divided by contribution margin per job. Break-even revenue equals fixed costs divided by the contribution margin ratio. A higher contribution per job means fewer jobs are needed to cover fixed costs.