Why eBay results are estimates
eBay’s final value fee depends on the category, your store subscription, seller performance level and the total amount of the sale, which includes shipping and, in the US, sales tax. International sales, promoted listings and currency conversion add further charges. These calculators let you set each of those rates, so the result matches your situation as closely as possible.
For exact figures, compare with the fee breakdown on a completed order in Seller Hub. If a category has a different rate from the default, change the final value fee field to match.