Sources
We start from Amazon: its seller fee pages, announcements and published examples. Where Amazon's page needs a Seller Central sign-in, we use independent copies of the same rate card and only publish a figure when at least two agree, or when it reproduces Amazon's own examples. Every source is listed on the page that uses it and on the methodology page.
Labels
Each number is labelled: Amazon for published rates, Derived for values computed from published rates by a stated rule, Estimate for our assumptions. We never present an estimate as a published rate.
Testing
The fee engine has automated tests built from published examples. A change to any fee value has to pass them, and a newly found example becomes a new test. Guides compute their figures from the same engine, so text and calculator can't drift apart.
Updates
We recheck fee data whenever Amazon announces a change and at least once a quarter. Each page shows when it was last checked; every data change is logged in the changelog.
Corrections
If you find a number that disagrees with your Seller Central fees, email [contact email, set at launch]. We investigate, fix confirmed errors, add a test and note the correction in the changelog.
Independence
We don't accept payment to change results, rankings or recommendations. If we ever add affiliate links or sponsorships, they will be disclosed where they appear and never placed inside calculator results.
Who we write for
Amazon sellers making real decisions about products, prices and fulfillment. We write plainly, show our working, and leave out anything that wouldn't help them.