Contribution Margin Decisions
A framework for converting contribution margin into the daily decisions that actually move profit — what you can pay for traffic, when to discount, and which SKUs to scale.
Contribution Margin Decisions
The operating playbook contribution margin unlocks: break-even ROAS, bid ceilings, free-shipping thresholds, discount floors, and SKU/channel scaling rules.
Contribution margin is the revenue left after variable costs — COGS, payment fees, picking, packing, shipping, and returns reserve. On its own, the number is interesting. The point is what it lets you decide.
Contribution margin decisions are the operating rules a store derives from that number: the maximum ROAS you can lose money at and still grow, the discount depth that turns a campaign unprofitable, the basket size at which free shipping pays for itself, and the SKUs that deserve more ad budget versus the ones quietly draining it. Treat the metric as the input; treat the decisions as the output.
Most stores compute contribution margin once a quarter, paste it into a board deck, and then run acquisition, pricing, and merchandising as if it didn't exist. That's where the money leaks. Every paid bid, every Klaviyo promo, every free-shipping banner is implicitly making a CM assumption — usually the wrong one.
This framework converts a single number — your contribution margin percentage — into five decisions you make every week. Read it as a checklist of guardrails, not a spreadsheet. The point is to stop deferring to gut feel when the math is straightforward.
Acquisition decisions: what you can pay for a customer
The first and most expensive decision contribution margin governs is your acquisition ceiling. Your break-even ROAS is simply 1 divided by your contribution margin percentage. At 40% CM, break-even ROAS is 2.5; at 25% CM, it climbs to 4.0. Below that line, every new order loses cash on the first purchase.
That gives you three operational levers. A bid floor (the ROAS below which Meta or Google campaigns get paused), a target ROAS (typically break-even × 1.3-1.5 to fund overhead and growth), and a CAC payback window — the months of repeat purchases needed to recoup acquisition cost. Stores with strong repeat behaviour can deliberately bid under break-even ROAS; stores selling one-shot SKUs cannot.
Pricing and promotion decisions
Every discount eats contribution margin point-for-point. A 20% off code on a product carrying 35% CM doesn't reduce profit by 20% — it reduces contribution margin to 15%, a 57% cut to per-order profit. This is the calculation most merchandisers skip, and it's why Black Friday weeks regularly print revenue records and cash losses simultaneously.
Free shipping is the same trap in slower motion. If average shipping cost is €7 and contribution margin on a €60 order is €21, a free-shipping offer at €60 burns a third of your CM. Set the threshold using a free-shipping threshold calculator: the basket size at which incremental margin from upsold units exceeds the shipping subsidy.
Don't confuse contribution cost with full cost
Contribution margin decisions use variable costs only — COGS, fees, fulfilment, returns. Fixed overhead (rent, salaries, software, brand spend) does NOT belong in the per-order math. If you load full costs into your break-even ROAS, you'll set a bid ceiling that's structurally impossible to hit and starve growth. Cover overhead at the portfolio level, not the unit level.
Assortment and channel decisions
Run contribution margin at the SKU level and the picture changes. In most apparel and beauty catalogues, 20-30% of SKUs carry CM below 15% once returns and fulfilment are properly allocated. Those SKUs are candidates for price increases, supplier renegotiation, bundling into higher-CM kits, or quiet delisting. Don't ad-spend behind them.
The same logic applies to channels and markets. A Shopify Markets expansion into a country with higher shipping and FX-driven COGS can drop CM by 8-12 points versus the home market — meaning your Meta target ROAS in that country needs to be materially higher. Channel-level contribution margin benchmarks are the input to whether you scale a channel, hold it flat, or pull budget.
Decision thresholds across contribution margin tiers
Frequently asked questions
Your break-even ROAS — the ROAS below which you lose cash on every new order. It's simply 1 divided by your contribution margin percentage, and it sets the ceiling for every paid acquisition campaign. Without it, ad bidding is guesswork.
No. Contribution margin uses variable costs only: COGS, payment processing, picking, packing, shipping, and returns reserve. Fixed costs (rent, salaries, software, brand campaigns) get covered at the portfolio level once enough contribution dollars are aggregated.
Discounts compress contribution margin point-for-point, which raises break-even ROAS proportionally. A 20% promo on a 40% CM product cuts CM to 20% and raises break-even ROAS from 2.5 to 5.0. The ad budget that was profitable on full-price orders is now structurally underwater on promo orders.
Take your average shipping cost, divide by your contribution margin percentage, and that's the minimum basket size at which free shipping breaks even on the next order. Most stores then add 15-25% headroom to fund the AOV lift that justifies the offer. A free-shipping threshold calculator does this with one input.
Yes — if repeat behaviour is strong enough to recoup the loss inside your CAC payback period. A subscription-style brand with 60% 90-day repeat can bid below break-even on first orders. A single-purchase home-goods store cannot. The CAC payback period decides.
Monthly at minimum, weekly during promo seasons. COGS shifts with supplier price changes and FX. Shipping costs change with carrier renegotiations. Returns rates drift seasonally. A CM figure older than a quarter is usually 3-5 points off reality — enough to misprice every campaign.
Apparel and beauty typically run 35-50% blended CM, electronics and home 20-35%, digital and accessories 55-75%. The right target is whatever leaves you a break-even ROAS your channels can realistically hit. Contribution margin benchmarks by vertical give you the comparison.
When the SKU's CM is below 15% AND it doesn't function as an entry product, bundle anchor, or restock driver. Pure tail SKUs with weak attach rates and weak CM should be cut — they consume merchandising attention, inventory cash, and ad spend that better SKUs would convert more efficiently.
Yes. A proper CM calculation reserves for returns at the historical rate for that SKU or category, including return shipping, restocking labour, and write-downs on damaged returns. Apparel CM that ignores a 25-30% return rate overstates true contribution by 8-12 points.
Contribution margin is the numerator of CAC payback. Payback months = CAC divided by (average monthly contribution per customer). Improving CM directly shortens payback — a 5-point CM lift can shave 1-2 months off payback at constant CAC, which usually matters more than chasing lower CAC.
Track CAC, channels, and funnel conversion in one place
Metricuno connects ad spend, funnel events, and revenue so you can see CAC by channel, cohort, and campaign — without stitching together five tools.