Methodology
Where every number on this site comes from, and how we keep it current.
Sources
Every rate a calculator uses is copied by hand from an official page: the marketplace's own fee schedule, or the customs authority's published tariff. We do not use third-party summaries, forum posts or our own estimates. Each data entry stores the URL it came from and the date it was checked.
Dates on every page
The line under each tool shows when its data was last verified. When a page uses many rates, the date shown is the oldest one, so every number on the page was checked on or after that day. If that date is more than 90 days old the page says so.
Changes
When a marketplace or customs authority changes a rate, we update the entry, set a new verified date, and record the change on the changelog.
Converters and validators
Conversion and validation rules follow each platform's published import documentation. Before a tool is published, it is run against real store exports, and the expected results for each test file are kept with the source code.
Limits
Calculator results are estimates for planning. Duty depends on the exact HS code, origin rules and valuation, so confirm import costs with a licensed customs broker before you rely on them.