All calculators

How these calculators differ from a percentage in a spreadsheet

Every tool here runs a real fee schedule rather than an average, and that distinction does most of the work. A spreadsheet multiplying a sale price by a platform's headline rate will be close on a typical order and wrong in the three places that matter most: where the fee is charged on a base that includes the postage you collected, where a fixed per-order amount dominates a small sale, and where a tiered schedule steps at a threshold instead of sloping through it.

The engines behind these pages model those cases explicitly. Where a schedule has a discontinuity, the page names the price it happens at rather than drawing a smooth line through it. Where a fee applies to shipping as well as the item, that appears in the stated fee base rather than being folded into an effective percentage.

Where the numbers come from, and how you can check them

Rates are read from each platform's own published fee page, or from the relevant revenue authority for the tax tools, and every page carries a "Sources and dates" section naming what was used and when it was last checked. That date is the honest limit of the figure. A schedule can change the day after it is verified, and a calculator that will not tell you when it last looked is asking to be trusted further than it has earned.

Each page also lists what it does not model. Those are not disclaimers for their own sake — they are the specific cases where the answer will be wrong, written down so you can tell whether yours is one of them.

What happens to the numbers you type

They stay on your device. Every calculation runs in JavaScript in your own browser: there is no account, no form submission, and no figure you enter is transmitted or stored anywhere. The page fetches its rate data once when it loads and then does all of its arithmetic locally, so changing an input sends no request at all.

To be precise about what the page does load: these calculators are funded by advertising, so an ad script loads alongside the page and sets cookies of its own. That is the one third-party request on the site, it is unrelated to the calculator, and it never receives the values you enter. The privacy policy sets out exactly what it does.

Which calculator should I start with?

If you already know the platform, use its own calculator — it models that schedule in full and will be the most precise. If you are choosing between platforms, start with a comparison page, because the answer frequently depends on your price point rather than being fixed. If you are self-employed and the question is what you owe rather than what a platform takes, start in the freelance section. Otherwise the filter above sorts every tool by category.