One sale, every platform. Type the price, the shipping the buyer pays, your label cost and what you paid for the item.
Category rates, promoted listings and store subscriptions change the numbers: check each platform's fee page.
The Reseller Profit & Inventory Tracker does this and much more in Google Sheets and Excel: saved, organized and protected so nothing breaks. Buy once, $12.
See the Reseller Profit & Inventory Tracker