How these numbers are made
Every rate on this site is read from the organisation that charges it, stored with the URL it came from and the date it was read, and checked by the build before it can ship. This page sets out that process in full, including the parts of it that are weaker than you might assume.
Where does each rate come from?
Primary sources only. A marketplace fee comes from that marketplace's own published fee page or rate card; a tax figure comes from the revenue authority that sets it. Nothing here is copied from another calculator, a summary article, or a competitor's page — not because those are always wrong, but because a figure with no traceable origin cannot be re-checked when it changes, and rates change constantly.
Each rate file records, for every source it draws on, a label, the exact URL, and the date that URL was read. That third field is the one most sites omit. A fee schedule without a retrieval date is a claim about the present tense that nobody can date, which makes it impossible to tell a current figure from a stale one.
What the build refuses to publish
The provenance rules are enforced by the build rather than by intention. Before the site is generated, every rate file is checked for three things:
- a version, so a change to a schedule is a distinct thing that can be pointed at;
- an effective date — the date the schedule itself came into force, which is not the same as the date it was read;
- at least one source, each carrying both a label and a working URL.
A file missing any of these does not produce a warning. It fails the build, and the site does not generate. This is deliberate: a check that can be ignored under time pressure is a check that will be, and the failure mode it guards against — a plausible-looking number with no origin — is invisible once shipped.
What "verified" means here, and what it does not
Passing the provenance check is not the same as being confirmed correct. Those are tracked separately, and each rate file carries one of three states:
- Needs verification — the figures are entered and sourced, but no one has yet sat down with the primary source and confirmed them line by line.
- Partially verified — some tables in the file were confirmed against the source and others were not.
- Verified, carrying the date it was confirmed.
Partially verified counts as unverified. A file where the commission table was checked but the fulfilment tables were not still contains an unchecked number, and treating it as done is precisely how that number survives to be wrong later. Only a full confirmation with a date clears a file from the internal checklist.
This distinction is the honest limit of the site. "Sourced" means the number can be traced. "Verified" means it was read back against the source on a stated day. The two are not interchangeable, and anywhere a figure is still pending confirmation the page carrying it says so rather than presenting it as settled.
Why a correct rate can still go stale
Platforms change their fees, sometimes with little notice and sometimes without updating every page that documents them. A retrieval date is therefore not a guarantee that a figure is current — it is a statement of the last moment anyone could show that it was. The gap between that date and today is a real source of error, and it is published on every page for exactly that reason.
This is also why the calculators state the fee base and the arithmetic rather than only the result. If a rate has moved since it was last read, a visitor who can see the formula can substitute the new number and still get a correct answer. A page that shows only its output leaves them with nothing.
What to do when a number here is wrong
If a figure on this site disagrees with what a platform actually charged you, the platform is right and this site is wrong. That is not a disclaimer — it is the operating assumption, and reports are handled on that basis.
Use the report button on the contact page. The single most useful thing to include is the discrepancy itself: what the calculator said, what you were actually charged, and the sale price or invoice amount that produced it. A screenshot of the platform's own fee breakdown settles almost every case immediately.
What happens next:
- The figure is checked against the primary source, not against the report. A report is what prompts the check; the source is what decides it.
- If the source has changed, the rate file is updated, its version incremented, its effective date moved to the date the new schedule took force, and its verification state reset — a corrected file is not automatically a confirmed one.
- If the source has not changed, the error is in the arithmetic rather than the data, which is a code fix and gets a test that reproduces the wrong answer first.
- Either way the page's last-updated date moves, so the change is visible rather than silent.
- If a figure cannot be confirmed either way — a source behind a login, a regional page that will not load, a schedule that contradicts itself — it is marked as unconfirmed rather than guessed at.
There is no support desk and no guaranteed response time here. What there is instead is a commitment that a reported discrepancy is checked against the primary source rather than dismissed, and that when this site is wrong the correction is dated in public rather than edited away quietly.
What these calculators deliberately do not do
They estimate. They are not a quote, not a bill, and not a substitute for the figures a platform or a revenue authority gives you directly. Every calculator carries its own list of what it does not model — those lists are specific on purpose, so you can tell whether your situation is one of the cases where the answer will be wrong. The disclaimer sets out the limits in full.
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