Guides and analysis

What gets written here

Posts are written when a published rule changes and the change costs somebody money. A divisor moves, an exemption is withdrawn, a fee schedule is restructured — and the arithmetic that everyone had settled on quietly stops being right. That is the trigger. There is no publishing calendar, because rate changes do not have one.

Each one is written from the primary document rather than from other people's summaries of it: the DMM revision, the Council Regulation, the Federal Register notice, the carrier's own service guide. Where the primary source sits behind a login — Amazon's FBA rate card is the standing example — the post says so and marks the figures as a secondary reproduction rather than implying a precision we do not have. Where something is genuinely unsettled, the post says that too, instead of picking a number and presenting it as fact.

Why the two dates on every post

Every post carries the date it was published and the date it was last checked, because on this subject those are different things and only one of them is useful. An article about import duty written accurately in June 2026 was wrong by July. A published date tells you when somebody wrote it; a checked date tells you whether anybody has looked since.

Where a post is superseded by a rule change it gets corrected rather than quietly left up, and the correction is dated. If a figure here disagrees with your invoice, your invoice is almost certainly right and we would like to know — the contact page explains what makes a correction easy to act on, and the source register records when each figure was last verified.

How these relate to the calculators

Each post names the calculators it applies to and links them, and each of those calculators links back to the posts that explain its subject. The division of labour is deliberate: a calculator answers the question for your numbers, and a post explains why the rule is what it is and what changed. Neither is much use on its own — a figure without its reasoning cannot be checked, and reasoning without a calculator leaves you doing arithmetic that is easy to get wrong.