Why "price minus cost" is not your profit
Most sellers start with a simple sum: I buy it for $12, I sell it for $40, so I make $28. That number feels reassuring, and it is almost always wrong. It ignores every party that touches the transaction between the customer clicking buy and the money landing in your account.
Real per-order profit is what remains after you subtract product cost, inbound freight and duty, packaging and pick-and-pack, platform and referral fees, payment processing, the shipping you actually pay, the expected cost of returns, and advertising. Only then do you have contribution profit — the amount each sale adds before fixed overhead. Fixed costs like your subscription, apps, rent, and salaries come off after that.
The Ecommerce Profit Calculator runs one order through this exact pipeline. Understanding the pipeline matters more than the tool: if you know which layer eats the money, you know which lever to pull.
The layers, in the order they subtract
Start with what the customer's card is charged — the gross charge. This is the item price plus any shipping you bill them and any add-ons, after discounts. Percentage fees are calculated on this number, not on your cost, which is why fees quietly scale with price.
Goods cost comes next: the unit cost plus inbound freight and any import duty. Then fulfilment — packaging and the labour to pick and pack. Then two fee layers that catch people out: platform or marketplace fees (a referral percentage plus flat listing or closing fees) and payment fees (a processor percentage plus a fixed per-transaction charge, plus any chargeback allowance).
Shipping is the cost you pay the courier, which is separate from whatever you charged the customer. Returns are modelled as an expected loss: even if only a fraction of orders come back, the cost of those returns is spread across every order as an allowance. Finally, advertising — whether you enter it as spend per order, a customer acquisition cost, or derive it from a target ROAS.
A full worked example, one order at a time
Take the calculator's default DTC product: a $40 item, $4.95 shipping charged to the customer, sold on an own-store setup with a 2.9% + $0.30 payment fee, 4% return rate, and $6 of ads per order.
Add it up layer by layer against a gross charge of $44.95 (the $40 item plus $4.95 shipping):
Worked example
From per-order to the month
Contribution and net profit per order are the honest single-sale numbers, but a business runs on the month. At 600 orders, that $15.51 of contribution becomes about $9,304, and after the $3,000 of fixed overhead the business nets roughly $6,304 for the month.
This also tells you your break-even volume. Fixed costs of $3,000 divided by $15.51 of contribution per order means you need about 194 orders just to cover overhead — every order beyond that adds its full contribution to the bottom line. If your realistic monthly volume is well above that break-even, the product can scale; if it is close to or below it, the economics are fragile.
You can see the same math laid out interactively in the Ecommerce Profit Calculator, including how the monthly figure moves as volume changes.
Own-store vs marketplace: the same order, different fee structure
The worked example above uses an own-store setup (0% platform fee, a standard payment gateway). Run the identical $44.95 order through a typical marketplace fee structure instead — a 15% referral fee plus a $0.25 closing fee, replacing the separate payment-processing charge — and the picture changes: platform fees jump to $44.95 × 15% + $0.25 ≈ $6.99, versus $1.60 of payment fees on the own-store version.
With every other line held constant, total variable cost rises to $34.83 and contribution falls to $10.12 (22.5% of revenue) — about $5.39 less per order than the own-store version's $15.51. Neither channel is universally better: a marketplace often brings built-in demand and can need less ad spend to reach the same volume, which can offset a chunk of that fee gap. The honest comparison runs the full per-order pipeline for both channels at your own realistic ad spend for each, not just the headline fee percentage.
Where advertising fits: break-even ROAS
Ads are usually the largest and most volatile variable cost, so it helps to know how much ad revenue you need per dollar spent just to avoid losing money. That figure is break-even ROAS.
In the example, contribution before ads is $15.51 + $6.00 = $21.51. Dividing the $44.95 gross charge by that gives a break-even ROAS of about 2.09 — meaning every $1 of ad spend must return at least $2.09 in sales for the order to stay above water. Run ads below that ratio and each incremental order loses money.
This is worth checking on its own before you scale spend. The Break-Even ROAS Calculator isolates that single ratio, and the underlying method is described on our methodology page.
What a subscription model changes
Everything above models a single, one-time order. A subscription or repeat-purchase business changes the math in one important way: acquisition cost gets spread across the lifetime of a customer relationship, not just the first order. A first order that loses money on paper — because the full ad cost of acquiring that customer is charged against just one sale — can still be a good decision if the customer is expected to place several more orders, or renew a subscription, at little to no further acquisition cost.
This is the same idea behind customer lifetime value (LTV) and the LTV:CAC ratio: instead of asking whether this order alone covered its ad cost, the question becomes whether the ad cost pays for itself across everything this customer is expected to spend over time. A per-order calculator like this one is still the right starting point — it tells you the per-order contribution before ads — but a subscription or repeat-heavy business should also model the lifetime picture with a dedicated LTV:CAC calculator before writing off a first-order loss as a failure.
Reading the margin you actually keep
The example carries a 34.5% contribution margin but only a 23.4% net margin after overhead — and that is a relatively healthy product. Plenty of ecommerce products land in single-digit net margins, where one fee increase, a small return spike, or a rise in ad costs can wipe out the profit entirely.
There is no universal "good" margin; it varies enormously by category, price point, and channel. A high-priced, low-return item can thrive on a slim percentage, while a cheap, heavy, returns-prone product can be unviable at a margin that looks fine on paper. What matters is knowing your own number and how sensitive it is.
Common mistakes
- Charging percentage fees on your cost instead of on the gross charge — platform and payment fees are a slice of what the customer pays, so they grow as your price grows, not as your margin grows.
- Forgetting that shipping charged to the customer and shipping you pay the courier are two different numbers; billing $4.95 while paying $5.50 still leaves a shipping gap you absorb on every order.
- Treating returns as a rare exception rather than a recurring cost — even a 4% return rate is an expected loss that should be spread across every order, not ignored until it happens.
- Confusing contribution margin with net margin and celebrating the bigger number; overhead per order still has to come out before you have real profit.
- Leaving fixed costs like subscriptions, apps, salaries, and rent out of the calculation entirely, so the per-order figure looks far healthier than the business actually is.
- Judging ad spend by ROAS alone without checking break-even ROAS first, so you scale spend on a ratio that is quietly below the point where each order pays for itself.
- Comparing channel fees without also comparing the ad spend and demand each channel brings. A higher-fee marketplace can still net more if it needs less advertising to reach the same volume.