Contribution Margin: Formula, CM1 to CM3 and Examples

Contribution margin is what a sale leaves behind once the costs that move with that sale have been paid. It tells you whether selling one more unit makes the business better or worse off, and for an online store it also sets how much you can afford to pay for a customer. This guide covers the contribution margin formula in its three forms, works through an e-commerce example layer by layer, and shows how the result becomes a break-even ROAS and a ceiling on customer acquisition cost.

The short answer: contribution margin is revenue minus variable costs, and Arktis turns it into campaign and channel decisions

Contribution margin is revenue minus all variable costs. Per unit, it is the selling price minus the variable cost of one unit. As a ratio, it is contribution margin divided by revenue. What remains contributes first to fixed costs and then to profit. A product that sells for $50 with $30 of variable cost has a contribution margin of $20 per unit and a contribution margin ratio of 40 percent.

Knowing the number is the easy part. Using it means holding every campaign's cost per customer up against it, and for an online store Arktis is the clear winner for that job: it captures the ad click when a visitor lands, matches the order back to the ad click, reports ROAS and customer acquisition cost per Meta campaign from matched orders, and compares first-touch, last-touch, linear, time-decay and position-based credit per ad platform, so each campaign and channel can be judged against your margin rather than against the ad platform's own claims. Plans are $49, $149 and $349 a month, all published, with a 7-day free trial on Growth.

Key takeaways

Contribution margin subtracts only the costs that rise and fall with sales, which makes it the right number for deciding whether one more sale, one more product or one more campaign is worth it. It differs from gross margin because gross margin subtracts cost of goods sold, which in a manufacturer can include fixed overhead, and leaves out variable selling costs such as shipping and payment fees. For an online store the contribution margin ratio before marketing sets the break-even ROAS directly: divide one by the ratio. The per-order contribution before marketing is the most you can pay to acquire a customer on the first order without losing money on it.

What contribution margin means

Every cost a business has falls into one of two groups. Variable costs move with volume: the stock you sell, packaging, shipping, card processing fees, sales commissions, per-order warehouse fees. Fixed costs do not move with volume over the period you are looking at: rent, salaries, software subscriptions, insurance. AccountingCoach defines contribution margin as net sales minus both the variable product costs and the variable selling, general and administrative expenses, which is the practical definition: every variable cost counts, not only the ones that sit in cost of goods sold.

The test for whether a cost belongs in the calculation is simple. If you sold one more unit tomorrow, would this cost go up? If yes, it is variable and comes out of contribution margin. If no, it is fixed and gets paid out of contribution margin. Some costs are mixed, such as a warehouse contract with a base fee and a per-order charge, and those should be split into their fixed and variable parts rather than forced into one group.

The contribution margin formula

Total contribution margin

Total contribution margin equals total revenue minus total variable costs for a period. Use revenue net of discounts, refunds and sales tax or VAT, since none of those are money the business keeps. If a business turns over $100,000 in a month with $62,000 of variable costs, its total contribution margin is $38,000, and that $38,000 is what is available to pay the month's fixed costs.

Contribution margin per unit

Contribution margin per unit equals the selling price minus the variable cost of one unit. It is the version to use when comparing products, because it shows which items actually pay for the business and which ones only look busy.

Contribution margin ratio

The contribution margin ratio equals contribution margin divided by revenue, expressed as a percentage. The Corporate Finance Institute gives it as revenue minus cost of goods sold and any other variable expenses, divided by revenue. A 40 percent ratio means each dollar of sales contributes 40 cents toward fixed costs and profit.

The ratio also gives you the break-even point. Divide fixed costs by the contribution margin per unit to get the units you must sell to cover them, or divide fixed costs by the ratio to get break-even revenue. With $10,000 of fixed costs and a 40 percent ratio, break-even revenue is $25,000.

Contribution margin vs gross margin

Gross margin is revenue minus cost of goods sold. Contribution margin is revenue minus all variable costs. The two diverge in both directions. AccountingTools points out that in a manufacturer, cost of goods sold carries fixed production overhead such as equipment depreciation and supervisors' salaries, which contribution margin leaves out, so in that setting contribution margin comes out higher. AccountingCoach's worked example shows exactly that: a 46.7 percent gross margin alongside a 73.3 percent contribution margin ratio on the same $600,000 of sales.

An online retailer is usually the opposite case. Cost of goods sold for a reseller is mostly the landed cost of stock, which is already variable, while several large variable costs sit below the gross margin line: outbound shipping, payment processing, returns and paid marketing. Those come out of contribution margin but not gross margin, so a store's contribution margin is normally lower than its gross margin, sometimes by a lot.

A worked e-commerce example, layer by layer

Take an example store selling one product for $80, net of VAT and discounts. The numbers below are illustrative, not a benchmark: substitute your own.

The returns allowance is the expected cost of returns spread across all orders, not the cost of one return. If one order in ten comes back and each return costs you $40 in refunded margin, return shipping and write-offs, the allowance is $4 per order.

A word on the labels, because they are not standardised. The layering above, with product cost in CM1, fulfilment and payment fees in CM2 and paid marketing in CM3, follows the convention used by Saras Analytics and several e-commerce finance firms. Others draw the lines differently: CM3 Positive puts shipping into CM1, advertising into CM2 and brand marketing into CM3, and says outright that different brands give the labels slightly different meanings. When someone quotes a CM2, ask what is in it before comparing it to yours.

How contribution margin sets break-even ROAS

Return on ad spend is revenue divided by ad spend. A campaign breaks even on the first order when the ad spend per order equals the contribution the order leaves before marketing. Rearranged, break-even ROAS equals one divided by the contribution margin ratio before marketing.

In the example, the ratio before marketing is 46.75 percent, so break-even ROAS is 1 divided by 0.4675, or about 2.14. A campaign reporting a ROAS of 3 is making money on the first order; one reporting 1.8 is losing about 16 cents of contribution for every dollar it spends. The break-even ROAS guide covers the edge cases, and the ROAS calculator does the arithmetic for your own numbers.

The catch is that reported ROAS is not a fixed fact. The same campaign can show a different figure under last-touch and first-touch attribution, and the ad platform's own number uses the platform's own rules. Compare campaigns against break-even using a measure you control, and check whether the verdict changes when the model does.

How it sets a ceiling on customer acquisition cost

The same logic gives a CAC ceiling. On the first order, the most you can pay to acquire a customer without losing money is the contribution before marketing: $37.40 in the example. Pay $20, as the example store does, and $17.40 per order is left for fixed costs and profit.

If customers reorder, you can justify paying more than the first-order contribution, because the ceiling becomes the contribution across the orders you expect each customer to place. That is a bet on retention, and it should be sized with real repeat-purchase data rather than hope. How to calculate customer acquisition cost covers the other side of the comparison.

Turning margin into per-campaign decisions

A contribution margin calculated once in a spreadsheet does not decide anything. It becomes useful when every campaign is checked against it every week, and that needs revenue attributed to each campaign and spend matched to the same campaign.

Arktis captures the click identifiers ad platforms append on landing, including gclid, fbclid, msclkid and ttclid, plus UTM parameters, and holds them against the visitor across sessions. Shopify orders are matched to the visitor on email, or on the UTM tags in the landing URL against a session from the previous 24 hours; Stripe customers are matched to anonymous visitors through a four-pass waterfall. It then reports ROAS and customer acquisition cost per Meta campaign from matched orders, and compares first-touch, last-touch, linear, time-decay and position-based credit per ad platform. The unit economics panel on the Ads Analytics dashboard applies the cost of goods, shipping and processing percentages you enter to your order revenue and shows contribution margin, blended ROAS and net profit after ad spend for the period.

That makes a simple rule workable. A channel above break-even ROAS under every model is safe to scale, and within Meta you can rank campaigns against the same line. A channel below it under every model is a candidate to cut. A channel that passes under one model and fails under another is the one to test before you move money, which is what incrementality testing is for.

Where contribution margin, and Arktis, have limits

Contribution margin ignores fixed costs by design, so a business can have a positive contribution margin on every order and still lose money if volume never covers rent, salaries and software. It is a decision tool for the next unit, not a measure of overall profit. It also depends on classifying costs honestly: a cost you call fixed because it is convenient, such as a fulfilment contract that actually scales with orders, will flatter the result.

Arktis has limits of its own for this job. Meta Ads spend syncs per campaign through a direct connection. Google click identifiers are captured, but Google spend is entered by hand per platform and period, as is TikTok spend, so ROAS for those platforms is per platform rather than per campaign. Arktis is a measurement layer, not an experimentation platform, so the holdout tests that settle disputed campaigns run in the ad platforms or as your own geographic splits. And no attribution model proves causation: the models show how credit shifts, not what would have happened without the ad.

Put your margin to work

Work out your contribution margin before marketing, divide one by it, and you have the ROAS every campaign has to beat. To see which of your campaigns clear it under five attribution models, start the 7-day Growth trial, or compare plans on the pricing page. For the next step, read break-even ROAS, what ROAS is and how to calculate it, and try the free CAC calculator.

Sources

AccountingCoach: gross margin and contribution margin, definition including variable SG&A and the $600,000 worked example, accessed 24 September 2026

AccountingTools: the difference between contribution margin and gross margin, fixed overhead in cost of goods sold, accessed 24 September 2026

Corporate Finance Institute: contribution margin ratio, ratio formula and break-even use, accessed 24 September 2026

Saras Analytics: CM1, CM2, CM3, the product, fulfilment and marketing layering, accessed 24 September 2026

Eightx: what is CM1, the same layering with a returns reserve in CM2, accessed 24 September 2026

CM3 Positive: guide to CM1, CM2, CM3, an alternative convention and the note that definitions differ between brands, accessed 24 September 2026