Fixed vs variable costs is the split between costs that stay the same as sales volume changes, such as rent, R&D salaries and software seats, and costs that rise and fall with volume, such as hosting usage, payment processing and commissions. Semi-variable costs mix the two. The split sets contribution margin, break-even and operating leverage.
Most guides list rent, materials and shipping and stop there. A software company's P&L looks different: very few true variable costs, a lot of people cost that moves in steps, and several bills that are part fixed and part usage. This entry sorts a B2B SaaS cost base line by line, answers the salaries and insurance questions properly, splits a mixed cost with the high-low method (with a calculator), and shows how the split changes contribution margin, break-even and operating leverage. To turn the split into a break-even point, use ORM's break-even calculator.
Fixed vs variable costs at a glance
A fixed cost stays flat in total as volume changes; a variable cost stays flat per unit. Both statements hold only within a normal range of activity and a set period. Over a year or two, nearly every cost can change.| Fixed costs | Variable costs | Semi-variable (mixed) costs | |
|---|---|---|---|
| Total cost when volume rises | Stays the same | Rises in proportion | Rises, from a base above zero |
| Cost per unit when volume rises | Falls | Stays the same | Falls, toward the variable rate |
| At zero volume | Still paid | Zero | The fixed part is still paid |
| SaaS examples | Rent, R&D salaries, G&A team, annual software seats | Hosting usage, payment fees, API usage, commissions | Hosting with a committed minimum, support tools with a base fee plus overage |
| Drives | Break-even point and operating leverage | Contribution margin per customer | Both, once split |
| Formula | Total fixed cost = F | Total variable cost = V x units | F + V x units |
Fixed vs variable cost examples for a SaaS company
In a B2B SaaS company most of the cost base is fixed or step-fixed people cost. The truly variable costs are hosting usage, payment processing, third-party API usage and commissions. Benchmarkit's 2025 SaaS benchmarks put median spend at 37% of revenue on sales and marketing, 34% on R&D and 24% on G&A, with a median subscription gross margin of 81%. Those three operating lines are mostly salaries, which do not move when one more customer signs.| Cost | Behavior | Why | Usual P&L line |
|---|---|---|---|
| Cloud hosting | Semi-variable | Committed spend or reserved capacity is fixed; usage above it grows with customers and activity | Cost of revenue |
| Payment processing | Variable | Charged per transaction. Stripe's standard US card rate is 2.9% + 30¢ per successful domestic card charge, so the total moves with billings | Cost of revenue |
| Third-party API usage | Variable | Billed per call, per message or per record, so it follows product usage | Cost of revenue |
| Sales commissions | Variable | Paid as a rate on bookings or revenue | Sales and marketing |
| Support team | Step-fixed | Flat until ticket volume needs the next hire, then a new step | Cost of revenue |
| Sales rep base salaries | Step-fixed | Flat per rep; the company adds reps ahead of revenue | Sales and marketing |
| R&D salaries | Fixed | The team builds the product once for every customer | Research and development |
| Office rent | Fixed | Set by the lease, not by sales | G&A (often allocated) |
| Software seats for staff | Step-fixed | Priced per employee, so they step with headcount, not with customers | Mostly G&A, allocated by team |
| Marketing programs | Discretionary fixed | Fixed once committed for the quarter, cut fast when revenue disappoints | Sales and marketing |
Are salaries fixed or variable?
Base salaries are fixed. Commissions and bonuses tied to bookings or revenue are variable. A sales rep's pay is usually both, so split it: the base goes in fixed costs and the commission rate goes in variable costs.- Base salary and benefits: fixed. Paid whether the company sells $1 or $10 million that month. - Commissions: variable with bookings. A rate on what the rep closes. - Company bonuses on annual targets: treat as fixed for the year once the plan is set, and true them up when results land. - Hourly or per-project pay: variable, when hours follow volume. Contractors who deliver implementation projects are the SaaS case. - Headcount as a whole: step-fixed. See the next section.
Is insurance a fixed or variable cost?
Insurance is a fixed cost for planning purposes. The premium is set for the policy year and does not move with this month's sales. Some policies are priced on payroll, revenue or headcount and adjusted at renewal or audit, so over several years insurance behaves like a step cost. For a monthly contribution margin or break-even model, keep it in fixed costs.Step-fixed costs: how headcount moves
A step-fixed cost is flat across a range of volume and then jumps when volume crosses a threshold. Headcount is the main one in SaaS. A support team of ten can cover a certain number of customers; customer number one past that point costs a new hire, not a few dollars.Sales headcount is the step that matters most for plans, because reps are a fixed cost long before they produce. Pete Furseth, ORM's COO, puts it this way: "When you look at the actual data, it can take a seller 15 to 18 months to confidently hit quota" (insight board, q38). A rep hired this quarter is fixed cost for most of next year before carrying a full quota. His conclusion for planning is short: "Capacity has to be created before the business needs it" (q40). That means the fixed cost step comes first and the revenue comes later, which is why S&M as a share of revenue often rises in a year of heavy hiring.
In a model, treat step-fixed costs as fixed inside the period you are planning, and add the next step on purpose when the volume plan says you will cross it.
Semi-variable costs and the high-low method
A semi-variable cost has a fixed base plus a variable part, and the high-low method splits it using the months with the highest and lowest activity. Take total cost and activity (customers, users, API calls, tickets) for both months:| Step | Formula | Excel or Sheets | Example (illustrative) |
|---|---|---|---|
| Variable cost per unit | (High-month cost minus low-month cost) / (high activity minus low activity) | =(B3-B2)/(C3-C2) | ($57,000 - $48,000) / (900 - 600) = $30.00 per customer |
| Fixed cost per month | High-month cost minus variable rate x high activity | =B3-B5C3 | $57,000 - $30.00 x 900 = $30,000 |
| Forecast cost | Fixed cost + variable rate x planned activity | =B6+B5C4 | $30,000 + $30.00 x 1,000 = $60,000 |
| Cost per unit at plan | Forecast cost / planned activity | =B7/C4 | $60,000 / 1,000 = $60.00 |
Semi-variable cost calculator
Enter two months of one mixed cost. The calculator is prefilled with the illustrative example: a B2B SaaS company's monthly hosting bill at 600 and 900 paying customers.
This cost behaves like $30,000 a month of fixed cost plus $30.00 for each unit of activity. At 1,000 units it should run about $60,000, or $60.00 per unit. Put $30.00 per unit in variable costs for contribution margin and $30,000 in fixed costs for break-even.
How the split changes contribution margin, break-even and operating leverage
Classification decides three numbers: the contribution margin ratio, the break-even point and how much profit moves when revenue moves. Get a step-fixed or semi-variable cost wrong and the first two barely change, while the third, the one a plan depends on, is off by a lot.Worked example, illustrative numbers. A B2B SaaS company has 1,000 customers paying $1,000 a month, so $1,000,000 of monthly revenue. Its monthly costs are $940,000:
- Hosting $60,000, split by the high-low method above into $30,000 fixed and $30,000 variable - Payment processing $30,000 and third-party API usage $20,000, both variable - Commission expense $50,000, variable - Support team $80,000 (ten people), step-fixed - R&D salaries $300,000, S&M salaries and programs $250,000, and G&A including rent and software seats $150,000, all fixed
Operating income is $60,000, a 6% operating margin. Here is the same P&L classified two ways. The naive split puts all of hosting and the support team in variable costs because they "grow with customers".
| Correct split | Naive split | |
|---|---|---|
| Variable costs | $130,000 | $240,000 |
| Fixed costs | $810,000 | $700,000 |
| Contribution margin | $870,000 (87%) | $760,000 (76%) |
| Break-even revenue (fixed / CM ratio) | $931,034 (932 customers) | $921,053 (922 customers) |
| Degree of operating leverage (CM / operating income) | 14.5 | 12.7 |
| Operating income if revenue rises 10% | $147,000 | $136,000 forecast |
| Operating income if revenue falls 10% | -$27,000 | -$16,000 forecast |
That is the practical case for getting fixed vs variable right. Put your own fixed costs and contribution margin ratio into the break-even calculator to find your break-even revenue, and use the net profit margin calculator to see where the bottom line lands. The operating leverage entry works the same idea over a full year of growth, and gross margin vs contribution margin explains why the variable cost line is wider than COGS.
Common mistakes
- Calling everything that grows "variable". Support, sales headcount and seats grow with the business, but in steps you choose. Treat them as step-fixed. - Leaving mixed costs whole. A hosting bill with a committed minimum is part fixed. Split it before it goes into contribution margin. - Mixing up variable costs and COGS. COGS includes fixed lines such as the support team, and variable costs include lines outside COGS such as commissions. Contribution margin uses variable costs, gross margin uses COGS. - Using the wrong unit. Hosting may follow usage, payment fees follow invoices and commissions follow bookings. Pick the driver for each line. - Calling a cost fixed forever. Fixed means fixed for this period and this range of volume. Leases end, contracts renew and teams get resized.
Planning with the split
A cost model is only as good as the volume it is multiplied by. Variable costs follow the bookings and revenue forecast, and the next fixed cost step, usually a hire, has to be triggered from that same forecast early enough to ramp. ORM builds the bookings and ARR forecast those numbers hang on and targets 95% accuracy, so the variable cost line and the hiring plan start from the same number.
This entry explains cost behavior for planning and analysis. It is not accounting, tax or legal advice.
Sources
- Benchmarkit, 2025 SaaS Performance Metrics benchmarks: median S&M 37%, R&D 34% and G&A 24% of revenue; median subscription gross margin 81%.
- Stripe, pricing, checked November 10, 2026: 2.9% + 30¢ per successful transaction for domestic cards.
- Pete Furseth, ORM COO, ORM insight board, 2026 (q38, q40): seller ramp of 15 to 18 months; capacity has to be created before the business needs it.
- High-low split, break-even and operating leverage figures: arithmetic shown on this page, on illustrative numbers.
Frequently Asked Questions
What is the difference between fixed and variable costs?
A fixed cost stays the same in total when volume changes, within a normal range of activity and a set period. A variable cost moves in total with volume, so it is roughly constant per unit. Rent and R&D salaries are fixed for a SaaS company; hosting usage, payment processing and commissions are variable. Total cost is fixed costs plus variable cost per unit times volume.
What are 5 examples of variable expenses?
For a B2B SaaS company, five common variable expenses are cloud hosting usage, payment processing fees, third-party API usage billed per call, sales commissions, and contractor or partner fees for delivering implementation services. Each grows when customers, usage or bookings grow and shrinks when they fall. For a manufacturer the classic five are raw materials, packaging, shipping, piece-rate labor and sales commissions.
Are salaries fixed or variable costs?
Base salaries are fixed costs, because they are paid whatever the company sells that month. Commissions and bonuses tied to bookings or revenue are variable. A sales rep's pay is usually both: a fixed base plus a variable commission. Hourly or per-project pay that moves with volume is variable. Headcount as a whole is step-fixed, flat until volume forces the next hire.
Is insurance a fixed or variable cost?
Insurance is usually a fixed cost. The premium is set for the policy year and does not change when sales go up or down that month. Some policies are priced on payroll, revenue or headcount and adjusted at renewal or audit, which makes them step costs over a longer period. For monthly contribution margin and break-even, treat insurance as fixed.
What are semi-variable costs?
Semi-variable costs, also called mixed costs, have a fixed part that is paid at any volume and a variable part that grows with use. A hosting contract with a committed monthly minimum plus usage above it is one. A phone or software plan with a base fee plus overage is another. Split them with the high-low method so each part lands in the right place.
How does the fixed vs variable split change break-even?
Break-even revenue is fixed costs divided by the contribution margin ratio, which is revenue minus variable costs, divided by revenue. Move a cost from fixed to variable and the contribution margin ratio falls while fixed costs fall too, so break-even can barely move while the profit you forecast for a swing in revenue changes a lot. That forecast is where classification errors show up.
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