Start with one consistent unit of analysis
Choose whether the model represents one item, one order, one shipment or one reporting period. An order-level model should use order revenue, order-level payment charges and the average number of units in that order. A unit-level model should divide order charges across units before comparing margins. Mixing a unit product cost with an order-level shipping charge overstates or understates profit whenever basket size changes.
Use the same currency and tax basis for every input. A currency selector only changes display formatting; it does not convert exchange rates. If revenue excludes sales tax collected for an authority, costs should also be entered on the corresponding recoverable or non-recoverable basis. Document this choice so the result can be compared with bookkeeping later.
Separate revenue from pass-through amounts
Begin with the amount economically earned from the customer: item revenue plus any shipping income you retain, less seller-funded discounts and refunds. Taxes collected and remitted by a marketplace are usually not operating revenue for a management-margin view. Gift wrap, service charges and shipping income belong in revenue only when they are part of the seller economics being measured.
Refunds need their own treatment because some platform and payment charges are returned while others are retained. A simple model can use an expected return-rate allowance, but monthly reconciliation should replace that allowance with actual refunded revenue, retained fees, recovered inventory value and reverse-logistics cost.
Put variable marketplace charges in the correct layer
Marketplace charges may use different bases. A referral or transaction fee may apply to item price, shipping income or tax depending on the platform and market. Payment processing usually combines a percentage and a fixed amount per transaction. Listing, closing, regulatory, currency-conversion and fulfillment charges may be fixed, tiered or conditional. Do not collapse them into a single percentage unless the simplified rate is derived from your own representative order mix.
Presets are starting assumptions, not universal facts. Category, seller plan, country, fulfillment method and advertising enrollment can all change the result. Preserve the source date and make rates editable. When an official page changes, confirm the applicable rule before changing a production default.
Use contribution margin before allocating overhead
Contribution profit subtracts the costs that change with an order: product cost, marketplace charges, payment fees, pick-and-pack, outbound shipping, packaging, variable customer service and advertising. It answers whether another similar order creates cash contribution. Net profit goes further by allocating fixed salaries, software, rent, insurance, professional services and other period overhead.
Do not hide overhead inside product cost when comparing channels. Keep a channel contribution view for pricing and advertising decisions, then apply a documented allocation rule for company-level profitability. This makes it clear whether a weak result comes from unit economics or from a scale that is too small to absorb fixed costs.
Worked order example
Assume an order has a 60 USD item price and 5 USD shipping income. Product cost is 18 USD, packaging and fulfillment are 7 USD, outbound shipping is 9 USD, marketplace and payment charges total 10.50 USD, and advertising attributed to the order is 8 USD. Revenue is 65 USD, variable cost is 52.50 USD, and contribution profit is 12.50 USD, or 19.2% of revenue. If monthly overhead allocation is 4 USD per order, estimated net profit becomes 8.50 USD.
The example is a structure, not a benchmark. Replace every line with your own settlement, fulfillment and advertising data. Then test a return allowance, a higher ad cost and a lower selling price separately. Changing one assumption at a time reveals which variable creates the largest margin risk.
Reconcile estimates with actual settlements
At least monthly, export orders, platform settlements, advertising spend, refunds and fulfillment invoices for the same period. Map each actual charge to the model line, investigate unmapped deductions and compare estimated versus actual profit by marketplace and product. A persistent difference means the model is missing a fee, using the wrong base or allocating cost inconsistently.
- Keep the original source file and the date of every rate assumption.
- Compare contribution margin separately from allocated net profit.
- Review the highest-volume and lowest-margin products first.