The basic formula
Net profit margin is estimated profit divided by gross order revenue. For a seller, gross order revenue usually includes item revenue plus buyer-paid shipping, minus discounts. Estimated profit is what remains after subtracting product cost, fulfillment cost, platform fees, payment fees, returns, ads, and any fixed-cost allocation.
A practical ecommerce formula is: estimated profit = gross order revenue - product cost - shipping cost - packaging - payment fees - platform fees - returns allowance - ad cost - other variable costs - allocated fixed costs.
Step 1: Start with order revenue
Start with the amount the order brings in before pass-through taxes. If the buyer pays shipping to you, include it as revenue. If you offer a discount, subtract it. If sales tax is collected as a pass-through, keep it separate unless a payment processor charges a fee on that tax amount.
Step 2: Subtract product and fulfillment cost
Product cost should include the real cost to put the product in your hands: materials, wholesale cost, manufacturing, inbound freight, customs, or landed cost when relevant. Fulfillment cost should include seller-paid shipping, packaging, inserts, labels, and handling costs you actually absorb.
Step 3: Add platform and payment fees
Most sellers have at least one percentage fee and one fixed payment fee. Fixed transaction fees matter more on low-ticket orders because the same fixed amount consumes a larger share of revenue. For platform-specific fees, use the dedicated calculators and source ledger rather than assuming one generic fee stack.
Step 4: Include returns and ads
Returns and refunds are often irregular, but ignoring them makes margin look healthier than it is. A return allowance can be a fixed amount per order or a percentage of revenue. Ads should be included as average acquisition cost per order when you are evaluating paid traffic.
Step 5: Allocate fixed costs carefully
Monthly apps, subscriptions, tools, rent, and software can be allocated across expected monthly orders. This is not perfect accounting, but it helps prevent a product from looking profitable while the store loses money after overhead.
Common mistakes
- Using markup when you meant margin.
- Forgetting buyer-paid shipping is revenue and seller-paid shipping is cost.
- Ignoring fixed payment fees on lower-priced products.
- Leaving out returns, ad cost, packaging, and monthly app costs.
- Using platform averages instead of checking the actual fee rules for the selling channel.
Use the calculator
Use the Ecommerce Profit Margin Calculator to estimate profit, margin, markup, break-even item price, and target-margin item price with editable assumptions.