Methodology & Editorial Policy

Formulas are implemented from primary sources: regulatory standards, peer-reviewed literature, recognised textbook treatments, and official government publications. We do not use secondary sources (blog posts, other calculators) as formula references. Formula sourcing is separate from data sourcing — a correct formula can still be applied to approximate data, so the two are labelled independently.

Every reference dataset behind the tools carries one of three labels, recorded in a single registry and shown on each tool page, on the data sources page, and in the provenance field of every API response.

Sourced — the publisher's own figures, either fetched automatically from the publisher or transcribed by hand from the publication (e.g. Cboe VIX closes, US BLS CPI-U, WHO life expectancy).

Derived — computed by us from a real source using a stated method. The inputs are genuine, but the values shown are our calculation rather than a table the publisher printed (e.g. life-table survivorship fitted to WHO life expectancy).

Illustrative — curated estimates produced so the calculators behave realistically. These approximate a named publisher's figures but are not that publisher's figures, and should not be cited as them. Where a tool uses illustrative data, the tool page says so above the explanation.

Each dataset also records how it is refreshed: automatically from the publisher, manually by hand, or not at all. Illustrative datasets have no upstream source to refresh from, so they are marked as not refreshed rather than implying an update cycle that does not exist.

All tools are for educational and planning purposes. They are not professional financial, medical, legal, or tax advice. Results should be reviewed with a qualified professional before making significant decisions.

Where a tool is jurisdiction-specific (e.g. UK VAT, US income tax brackets), the jurisdiction and applicable tax year are labelled clearly on the tool page. Tools using international data note the coverage and any known gaps.

To report an error, use the support page. Include the tool URL, what you believe is incorrect, and a source reference if you have one. Confirmed corrections are applied and documented in the tool's git history. We do not silently update figures — corrections are recorded.