eCommerce Unit Economics: Contribution Margin, CAC, MER and Break-Even
eCommerce unit economics for store owners: contribution per order, max and target CPA, AOV, repeat rate, break-even and why platform ROAS misleads you.
Author: Mousa Alhelo · Published · 6 min read
Profit in an online store is not calculated only at the monthly level; it is calculated per order. A store that knows what it earns from each order after product cost, shipping, payment fees and advertising knows exactly how much it can spend to acquire the next customer. This article explains unit economics as we apply them at E-SAFQA to every ad account we manage: contribution margin, cost per acquisition, average order value, repeat rate, break-even, and why the ROAS shown by ad platforms misleads.
Why you start from one order, not the total
Monthly reports hide problems. A store with healthy sales may lose money on every order in one product category and earn well in another, so the total looks acceptable while half the ads waste money. Unit economics force you to look at each product or category separately, which allows precise decisions: which products deserve advertising, which need a higher price, a bundle or a pause.
The core formula: contribution per order
This is the formula we use before spending a single dollar on ads:
Contribution = price × (1 − payment fee rate − average discount rate) − unit cost − shipping cost
| Line | Illustrative example | Note |
|---|---|---|
| Selling price | 200 | What the customer pays |
| Payment fees | 3% | Varies by gateway and payment method |
| Average discount | 10% | The actual discount rate on orders, not the advertised one |
| Net after fees and discount | 200 × 0.87 = 174 | |
| Unit cost | 90 | Purchase or manufacturing cost |
| Shipping | 20 | What you actually pay after what the customer pays |
| Contribution | 64 | Maximum acceptable cost per acquisition |
The numbers are illustrative, to show the logic only. The important result: in this example, any ad that costs more than 64 per order loses money, however good the ROAS looks.
From maximum CPA to target CPA
Contribution is the ceiling, not the goal. If you spend the whole contribution on advertising, nothing remains for fixed costs and profit. Our rule: target CPA = 70% of maximum CPA. In the example above, the target is about 45, leaving about 19 per order to cover subscriptions and salaries and to make a profit. The ratio is adjusted per store: a product bought repeatedly can carry a higher ratio on the first order, while a one-time purchase needs a lower one. Turning this number into a budget is explained in how much ad budget an online store needs.
Average order value: the lever everyone forgets
Raising average order value (AOV) improves the whole equation with no extra ad spend: shipping and acquisition costs are spread across a larger value. If the average order in the example rises from 200 to 260 through a bundle or a free-shipping threshold, contribution rises by more than the price increase because shipping is fixed. The practical tools are bundles, free-shipping thresholds, tiered offers and smart pricing, covered in how to increase average order value.
Repeat purchase and customer lifetime value
If a customer returns twice a year, the acquisition cost of the first order is spread across three orders, and you can accept a higher first-order CPA. But be careful: do not build a budget on an expected repeat rate that has not yet been proven. Start with the first order alone; when real repeat data appears from the store after three to six months, recalculate. Cart recovery and repeat-purchase offers through WhatsApp Pilot (whatsapppilot.esafqa.com) are among the cheapest ways to raise repeat rate because they speak to a customer who already knows you.
Break-even: how many orders you need each month
Break-even = monthly fixed costs ÷ (contribution − actual CPA). If fixed costs are 5,000 a month and contribution after advertising is 19 per order, you need about 263 orders a month to break even. This number tells you before launch whether the project is realistic with your budget, and whether you must raise the price, raise AOV or cut costs first. Include all fixed costs: platform and app subscriptions, salaries, rent or warehouse, and accounting. See the cost of building an online store for the full list.
Why platform ROAS misleads
The ROAS shown by Meta or Google is the revenue the platform attributes to its ads divided by spend on that platform. The problem has three parts:
- Overlap: a customer who saw a Meta ad, then searched on Google, then bought is counted by both platforms, so their numbers cannot be added together.
- Cancelled orders: the platform counts the purchase the moment it happens, even if the order is later cancelled or refused at delivery.
- Revenue, not margin: a 3x ROAS on a product with a 20% margin is a loss; a 2x ROAS on a 60% margin product is a profit.
That is why we judge accounts by MER = actual store sales ÷ total ad spend across all platforms, and use platform ROAS for direction only. The details are in MER vs ROAS.
A simple sheet to build before the first campaign
| Column | Source |
|---|---|
| Product or category | The catalogue |
| Selling price and actual average discount | Store reports |
| Unit cost | Supplier or factory |
| Net shipping cost | Courier rate minus what the customer pays |
| Payment fees | The payment gateway |
| Expected return rate | Store history or a conservative estimate |
| Contribution, max CPA and target CPA | The formulas above |
Update the sheet monthly with real store numbers and compare the actual CPA of each product with its target. This sheet decides which campaigns scale and which get reviewed.
From our experience
Noor Alhuda, a Palestinian embroidery brand selling in US dollars to the United States, Canada and Australia, had prices that could not carry international acquisition and shipping costs. We restructured pricing and shipping based on order economics, and average order value rose from 122 to 153 dollars while MER improved by 30% within two weeks, with no increase in ad spend. The ads did not change; the equation did. Read the Noor Alhuda case study.
Conclusion
Online store profitability starts from the contribution of a single order. From it come the maximum CPA and the 70% target, it improves through higher AOV and repeat purchases, and it is judged by MER rather than platform ROAS. Build the sheet before the first campaign and update it monthly. If you want your ads managed by this equation, see E-SAFQA’s paid ads management service.
Send us your product prices and costs on WhatsApp and we will calculate your maximum acceptable cost per acquisition before you spend on ads.
Want this applied to your store?
E-SAFQA builds and runs Shopify stores and their ads. Message us on WhatsApp for a free audit.
Frequently asked questions
How do I calculate profit margin for an online store?
Calculate it per order: selling price multiplied by (1 minus payment fee rate minus average discount rate), minus product cost, minus shipping cost. The result is the contribution margin, what remains to cover advertising, fixed costs and profit.
What cost per acquisition is acceptable for my store?
The maximum CPA equals the contribution per order. The target CPA we work to is 70% of that ceiling, so that 30% of the contribution remains as profit after advertising.
Why does Meta ROAS differ from my actual store profit?
The platform attributes to itself every purchase inside its attribution window, and counts cancelled orders and orders other platforms also influenced. That is why we judge by MER: actual store sales divided by total ad spend across all platforms.
What is the break-even point for an online store?
The number of monthly orders whose combined contribution (after advertising) covers fixed costs such as subscriptions, salaries and rent. Calculate it before launch to know the sales volume you need to survive.