Sources policy

Sources help readers verify the rule, definition, rate, or evidence behind a calculator. A citation supports a specific part of a page; it does not mean the source has reviewed or endorsedAllcalcy.

Source hierarchy

When suitable material is available, we prefer:

1. Laws, regulations, government publications, and official statistical data.
2. Standards bodies and recognized professional or clinical organizations.
3. Original peer-reviewed research and systematic reviews.
4. Established educational institutions and specialist reference works.
5. Transparent industry publications for industry conventions not defined by a public authority.

Search summaries, unattributed articles, and marketing pages are not used as the sole support for a consequential factual claim.

Jurisdiction and effective dates

A source may be authoritative but still inapplicable to a user's location or date. Calculators based on law, tax, or regional policy should identify the jurisdiction and effective period. Pages using US definitions for an otherwise general model should say so.

Linking and quotation

We link directly to the supporting publication where practical and identify its publisher. We summarize sources in our own words and use brief quotations only when the original wording is necessary.

Review and replacement

Source-dependent pages are reviewed when rules change or a source is withdrawn. A newer source does not automatically replace an older one if the older publication remains the controlling standard, but the page should explain the applicable date.

Broken or questionable sources

Report an inaccessible citation, outdated rule, or source that does not support the claim through our contact page. We handle material problems under thecorrections policy.