Guide, 2026-11-05

How to calculate your real profit per order after marketplace fees

Sales figures feel good, but the number that pays you is profit. For a small online seller the gap between the two is made of several small deductions: commission, a payment processing fee, a fixed fee per order, the cost of the item, shipping you pay, and advertising. Here is how to calculate profit per order and per month in any spreadsheet.

Step 1: Start from what the customer paid you

Revenue for an order is the item price times quantity, plus any shipping the customer paid, minus any discount you gave. Keep refunds in their own column so you can see them rather than quietly editing the original sale.

Step 2: Enter the fees as rules, not as guesses

Each sales channel charges differently, and the charges change. Look up the current fee page of every platform you use and write the rules down: a commission percentage, a processing percentage, a fixed amount per order, and any listing fee. Give each rule an effective-from date. When a platform changes its fees, add a new rule with the new date instead of overwriting the old one, otherwise last year's orders are suddenly recalculated at this year's fees.

Step 3: Add your own costs

Per order you usually pay for the product (materials, wholesale cost or print cost), packaging and postage. Per month you pay for ads and perhaps other costs such as software. Keep these separate: ads are easier to judge as a monthly total than to split across orders.

Step 4: Calculate

Profit = revenue − fees − product cost − shipping cost − (share of) ads. Margin = profit ÷ revenue. Margin is the figure to compare across products and channels, because a $40 profit on a $400 sale is worse than a $10 profit on a $25 sale.

A worked example

A fictional seller on a fictional channel with these made-up fee rules: 10% commission on the item price, 3% processing on the item price plus shipping, and $0.30 per order. One order: a $30 item and $5 shipping paid by the customer, so revenue is $35. The item costs the seller $9 and postage costs $4.50.

Margin is $17.15 ÷ $35 = 49.0%. Now a month of 40 identical orders: profit is 40 × $17.15 = $686. Ads cost $120 that month, so profit after ads is $566, and the margin on $1,400 of revenue is $566 ÷ $1,400 = 40.4%. If you decide to set aside 25% of profit for tax (your own percentage, not advice), that is $566 × 25% = $141.50, leaving $424.50.

Notice what ads did: they took about 9 points of margin, from 49.0% to 40.4%. If the ads only brought in orders you would have received anyway, they are costing you real money.

Common mistakes

• Using last year's fee percentages for this year's orders.
• Forgetting the fixed per-order fee, which matters most on low-priced items.
• Ignoring shipping you pay when the customer paid less than the real postage.
• Leaving out refunds, so revenue looks higher than what you kept.
• Comparing products by sales instead of by profit per unit.
• Spending the whole month's takings and having nothing set aside when tax is due.

When a ready-made tracker saves time

With one product on one channel the table above is enough. With several products, several channels and fees that change on different dates, the date-based fee lookups are where a hand-built sheet tends to break. SellerBook is built for this: a sales ledger with one row per order line, fee rules with effective-from dates, a monthly P&L over 12 months, profit and margin per product and per channel, a tax set-aside at your percentage, and data checks for sales with no fee rule for their date. No platform fees are built in, so you enter them yourself from each platform's current fee page. It does not connect to any marketplace, does not track sales tax or VAT, uses one currency per file, and is not accounting or tax advice. Tested in Microsoft Excel for Windows (Microsoft 365).