2025-08-16 00:00:00 WhatNot Profit & Fee Calculator helps you calculate WhatNot seller fees, return on investment (ROI) and profit expected on every sale. We use up-to-date WhatNot fee percentages to give the user the most current information available. By understanding your WhatNot fees, profit and Return on Investment, you can focus on selling items that make you the most money for your time invested.