What is contribution margin?
Contribution margin is what's left from each sale after variable costs — the portion that contributes to covering fixed costs (rent, salaries, software) and then profit.
Contribution margin per unit = Selling price − Variable cost per unit
Contribution margin % = Contribution margin ÷ Price × 100
Price $50, variable cost $22 → CM = $28 per unit (56%). Sell 1,000 units → $28,000 total contribution margin to put toward fixed costs.
How to calculate contribution margin (step by step)
- Set selling price — what the customer pays per unit or order.
- List variable costs per unit — everything that increases when you sell one more (see checklist below).
- Subtract: price − variable cost = CM per unit.
- Optional: multiply CM per unit × units sold = total CM for the period.
- Plug into break-even: fixed costs ÷ CM per unit = units needed to break even.
Worked example: DTC skincare brand
| Item | Per order |
|---|---|
| Selling price (AOV) | $68 |
| Product COGS | $18 |
| Packaging + outbound ship subsidy | $6 |
| Payment processing (~2.9%) | $2 |
| Variable cost per unit | $26 |
| Contribution margin | $42 (61.8%) |
Monthly fixed costs (team, warehouse base, software): $21,000.
Break-even units = $21,000 ÷ $42 = 500 orders/month before profit.
If paid ads add $8,000/month and bring 200 new customers at $40 CAC, those customers must contribute enough CM to cover that spend — 200 × $42 = $8,400 CM from those orders, barely clearing ad cost before fixed overhead.
Contribution margin vs. gross profit vs. profit margin
| Metric | What it subtracts | Best for |
|---|---|---|
| Contribution margin | Variable costs only | Unit economics, break-even, pricing tests |
| Gross profit | Usually COGS only | P&L reporting, gross profit totals |
| Profit margin | All costs (fixed + variable) | Bottom-line health |
For many ecommerce businesses, CM per unit equals gross profit per unit when variable cost equals COGS. Add shipping subsidies and payment fees to variable cost when they scale per order — that is when CM is more accurate than gross margin alone for ad decisions.
Why marketers should know CM
Every unit sold adds CM dollars toward fixed costs and ad spend. If CM per unit is $28 and CAC is $35, you lose $7 on acquisition before fixed costs — unless LTV saves you. Contribution margin is the bridge between pricing and whether paid growth works.
Pair CM with break-even analysis before scaling budget: if break-even units exceed realistic traffic, fix price or variable cost first — not ad creative alone.
Variable costs to include
Ecommerce: product cost, packaging, outbound shipping subsidies, payment processing (~2–3%), marketplace fees if applicable. SaaS: hosting and support per account. Agencies: freelancer cost on billable projects.
Exclude fixed costs like rent, base salaries, and software that does not scale per unit — those are covered after CM accumulates across volume.