Key takeaways
- Contribution margin = AOV minus all variable order costs—not just COGS.
- Gross margin can look healthy while contribution is thin after shipping and fees.
- CAC payback and break-even MER both run on contribution %, not revenue.
- Promos that lift orders often cut contribution—track $ and % after discounts.
- Use the Ecommerce Simulator margin-first scenario to see payback move before you scale ads.
Definition
Contribution margin — revenue per order minus variable costs per order. It is what each checkout contributes toward marketing, fixed overhead, and profit. In ecommerce, variable costs usually include COGS, outbound shipping (net of what the customer paid), payment fees, expected returns, and per-order fulfillment—not rent, salaries, or brand campaigns allocated above the unit.
Contribution margin formula
Contribution margin ($) = AOV − COGS − net shipping − payment fees − returns − variable fulfillment
Contribution margin % = Contribution margin ÷ AOV
Break-even units (fixed costs) = Fixed costs ÷ Contribution margin per order
Break-even MER ≈ 1 ÷ contribution margin % (before fixed costs; see MER)
CAC payback (orders) ≈ CAC ÷ contribution margin per order
Example: $75 AOV, $27 COGS, $8.50 net shipping, $2.25 fees, $3.00 expected returns → contribution = $34.25 → 45.7% contribution margin.
Contribution margin vs gross margin
| Metric | Typical formula | What it answers |
|---|---|---|
| Gross margin | (Revenue − COGS) ÷ Revenue | Merchandise profitability |
| Contribution margin | (Revenue − all variable order costs) ÷ Revenue | What each order funds (ads, overhead, profit) |
| Net margin | Profit after all costs ÷ Revenue | Bottom-line P&L |
Order-level contribution is the core of ecommerce unit economics. Customer-level economics stacks contribution across repeat purchases and subtracts CAC.
What the number hides / common mistakes
- Gross margin labeled “margin” — shipping and fees live below COGS; the store looks profitable until contribution is calculated.
- Free shipping not netted — subtract only carrier cost without customer shipping revenue and contribution is wrong by $5–12 per order.
- Returns excluded — apparel and footwear need an expected return line; see refund rate.
- Promo AOV without promo cost — discounts sit in net revenue; contribution % falls even when order count rises.
- Blended SKU average — bundles and gifts-with-purchase pull COGS up; hero SKU contribution subsidizes losers only if you planned it.
- Positive contribution, negative business — fixed costs above the unit still need enough orders; read break-even point.
Worked ecommerce example
A pet accessories brand runs a month with 3,200 orders, blended AOV $58. Below is per-order variable economics (not fixed overhead).
| Line | Per order | % of AOV |
|---|---|---|
| AOV (after discounts) | $58.00 | 100% |
| COGS (landed) | −$21.50 | 37.1% |
| Gross profit | $36.50 | 63.0% gross margin |
| Net outbound shipping | −$6.80 | 11.7% |
| Payment fees (~2.9% + $0.30) | −$1.98 | 3.4% |
| Expected returns | −$2.90 | 5.0% |
| Pick-pack variable | −$1.40 | 2.4% |
| Contribution margin | $23.42 | 40.4% |
Gross margin 63% sounds strong; contribution 40.4% is what funds growth. Monthly contribution dollars ≈ 3,200 × $23.42 = $74,944 before marketing. They spent $48,000 on acquisition for 1,050 new customers → CAC $45.71. Payback ≈ $45.71 ÷ $23.42 ≈ 1.95 orders— workable if repeat is reliable, tight if not.
Break-even MER ≈ 1 ÷ 0.404 ≈ 2.48×. Revenue $185,600, marketing $48,000 → MER 3.87×—above break-even on variable contribution, but fixed costs ($62,000/month) need $62,000 ÷ $23.42 ≈ 2,648 contributing orders just to cover overhead. Contribution margin answered “is the order healthy?”; break-even answered “is the company big enough?”
Lever: raise free-shipping threshold so AOV moves to $64 with the same cart composition— COGS rises $1.20, shipping net falls $1.10, fees rise $0.17 → contribution ≈ $24.15 (+3%). That is more durable than a 15% off sitewide that lifts orders but cuts contribution to 34%. Model both in margin and break-even ROAS.
Break-even MER ≈ 1 / contribution margin % is a planning floor before fixed costs—at 40% contribution, MER below ~2.5× means marketing is not covering variable contribution on average.
Source: Growthegy operator practice; MER and unit economics glossaries (2026)
How to read contribution margin in the Ecommerce Simulator
The Ecommerce Simulator builds contribution from AOV, COGS, shipping, fees, and refunds, then connects to CAC and payback:
- Start with margin-first: lock last month’s AOV and variable cost lines until contribution $ and % match your export.
- Add ad spend and new customers; read CAC and payback in orders against contribution—not against gross margin.
- Change one lever: shipping threshold, COGS point improvement, or refund rate −2pp. Save before/after contribution %.
- Compare to slow-profit if first-order contribution is negative but you are betting on repeat—see how long cash waits for order two.
Contribution is the bridge between product P&L and acquisition. When ROAS looks fine but profit does not, the gap is usually here—read ROAS vs ROI next to contribution margin %, not instead of it.
Related terms
- COGS — largest variable line for most SKUs.
- AOV — top of the contribution stack.
- CAC and payback period — customer layer.
- MER — break-even uses contribution %.
- Break-even point — fixed costs ÷ contribution.
Back to the ecommerce glossary. Contribution margin is the order-level truth test—calculate it after shipping and fees, use it for payback and MER floors, and never scale ads on gross margin alone.