Small Business guide
Ecommerce Contribution Margin Explained
Measure the money each order contributes after variable costs but before fixed overhead.
Updated 22 July 2026 • Reviewed by Tools by Layna Editorial Team • General information only
Why this decision is easy to misread
Contribution margin is the amount left from net sales after costs that change with the order. It is the pool available to pay advertising, wages, software, rent and profit.
Gross margin usually stops at product cost. Ecommerce contribution goes further by including delivery, fulfilment, payment fees and expected return losses.
Ecommerce decisions should be based on contribution profit, not revenue or platform ROAS alone. GST, discounts, landed cost, fulfilment, payment fees, refunds, returns and acquisition cost all sit between a sale and cash available to cover overhead.
Attribution is also imperfect. Platform-reported revenue may include customers who would have purchased anyway, while store reports can miss the influence of earlier advertising. Use the calculator as a unit-economics model and compare it with actual cohort and payment data.
The calculation, step by step
Net sales ex GST
Use revenue the business actually keeps before variable costs.
In the calculator, this item should be entered separately so a change in net sales ex gst can be tested without hiding it inside another assumption. Keeping the input visible also makes later reviews and comparisons more reliable.
Landed cost
Include product cost, inbound freight, duty and inspection where applicable.
In the calculator, this item should be entered separately so a change in landed cost can be tested without hiding it inside another assumption. Keeping the input visible also makes later reviews and comparisons more reliable.
Fulfilment
Add packaging, pick-and-pack and outbound shipping paid by the business.
In the calculator, this item should be entered separately so a change in fulfilment can be tested without hiding it inside another assumption. Keeping the input visible also makes later reviews and comparisons more reliable.
Payment cost
Include percentage and fixed transaction fees.
In the calculator, this item should be entered separately so a change in payment cost can be tested without hiding it inside another assumption. Keeping the input visible also makes later reviews and comparisons more reliable.
Returns
Use an expected cost per order based on actual return behaviour.
In the calculator, this item should be entered separately so a change in returns can be tested without hiding it inside another assumption. Keeping the input visible also makes later reviews and comparisons more reliable.
Advertising
Contribution before ads sets the maximum sustainable CAC.
In the calculator, this item should be entered separately so a change in advertising can be tested without hiding it inside another assumption. Keeping the input visible also makes later reviews and comparisons more reliable.
Worked Australian example
If net sales are $81, landed cost is $27, fulfilment and shipping are $12, payment fees are $2 and expected returns cost $5, contribution before ads is $35. A $25 CAC leaves $10 contribution after ads.
At 500 orders, that is $5,000 to cover all fixed overhead. If fixed costs are $8,000, the business is still loss-making despite positive order contribution.
Decision checklist
| Step | What to confirm |
|---|---|
| 1 | Calculate contribution by product and channel. |
| 2 | Use actual fulfilment invoices. |
| 3 | Update expected return cost monthly. |
| 4 | Separate pre-ad and post-ad contribution. |
| 5 | Compare total contribution with fixed overhead. |
Use the calculator with this guide
Open Ecommerce Profit and Break-Even ROAS Calculator Australia
Start with GST-exclusive revenue and deduct landed cost, fulfilment, payment fees, expected returns and acquisition cost at an order level.
Use the linked calculator for ecommerce contribution margin explained with a documented base case. Save the output, then create a conservative case using the most uncertain input from the worked example.
The useful break-even point is the ad efficiency or selling price where contribution profit reaches zero after all variable costs. Record that threshold beside the headline result; it is often the clearest way to judge whether the decision has enough margin for error.
Common mistakes
- Stopping at gross margin.
- Ignoring fixed payment fees on low-value orders.
- Averaging products with very different returns.
- Treating free shipping as free to the business.
- Confusing contribution with net profit.
Questions to answer before acting
- Calculate contribution by product and channel.
- Use actual fulfilment invoices.
- Update expected return cost monthly.
- Separate pre-ad and post-ad contribution.
- Compare total contribution with fixed overhead.
Where ecommerce contribution margin explained depends on law, tax, eligibility, lending policy or a contract, verify the applicable rule with the official source. The calculator measures the consequence of the input; it does not establish that the input legally applies.
Record keeping and review
For this calculation, retain the evidence behind net sales ex gst and landed cost. Label each number as confirmed, quoted, estimated or stress-tested, and date the evidence so a later comparison does not silently mix figures from different periods.
Official sources
The sources below were selected for Ecommerce Contribution Margin Explained because they define the relevant measurement, rule or evidence base. Recheck dated rates, thresholds and official guidance before acting.
Related guides
Frequently asked questions
What is a good contribution margin?
It depends on fixed costs, order volume and growth strategy.
Is CAC a variable cost?
Yes for acquisition analysis, though some brand spend is harder to allocate.
Should discounts reduce sales before margin?
Yes. Use the amount actually paid.
How are exchanges treated?
Include shipping, handling and write-down costs based on actual outcomes.
Can repeat value be added?
Yes, as expected future contribution supported by cohort data.
Sensitivity check before acting
Stress-test discount rate, customer acquisition cost and returns together. Those inputs compound: a discount reduces revenue while fulfilment and many fees remain, and a higher return rate can erase the contribution left for advertising.
For Ecommerce Contribution Margin Explained, keep the base, conservative and stress cases together. The decision is stronger when it survives a realistic adverse change rather than depending on one precise forecast.
Bottom line
Contribution margin connects order economics with the monthly business; it is the bridge between gross margin and net profit.