Why the headline percentage is not the answer
Comparing marketplaces by their advertised rate misleads, because they do not charge on the same thing. Some charge on the item alone. Some include shipping. eBay, Facebook and most payment processing also charge on the sales tax your buyer pays, money you never keep. Some take a flat amount on small sales, which can be far more than the percentage suggests.
Who pays for shipping changes the picture just as much. On Poshmark, Depop, Vinted and Whatnot the buyer normally pays for the label, so your own shipping figure is not subtracted there. On the others, offering free shipping comes straight out of your profit. A marketplace with a higher rate can still leave you more once that is counted, and this calculator counts it.
A worked example
Take a $50.00 item that cost you $10.00, with a $8.00 label where you pay for it and 7% sales tax. Vinted leaves you the most at $40.00. eBay leaves the least at $24.32. That is a difference of $15.68 on the same item at the same price.
The biggest profit is not automatically the best choice. Buyers on each marketplace pay different fees of their own, and an item only earns a profit if it sells. Use this to set your floor, then list where the buyers are. Many resellers list on several and take the item down from the rest when it sells.
What this leaves out
Results use each platform's default category and starting rate tier. Open a platform's own calculator for category-specific rates, eBay Store pricing, and Whatnot's volume tiers. Income tax, supplies and your own time are not included, so a real margin will be a little lower. An ad rate only applies where a marketplace has a per-sale ad program, and Depop and Etsy use their own fixed rates.
Common questions
Which marketplace has the lowest fees?
It depends on the price and who pays for shipping. Vinted charges sellers nothing, and Depop charges only processing. Low-priced items change the order, because flat fees weigh more heavily on them. Try your own numbers above.
What is a good profit margin for resale?
There is no single number, since a fast-selling item at a thin margin can beat a slow one at a wide margin. Set a minimum profit in dollars that makes the item worth your time, then use the max buy price calculator when sourcing.
Why do you ask about sales tax?
You do not keep it, but several marketplaces charge their percentage on it, so it raises your fees. Change the rate to match where your buyers tend to be.