Where holiday data comes from

Every holiday entry traces back to an official publisher. Aggregator sites are a finding aid, never the source of record.

The source order we use

1. The government itself: OPM for US federal holidays, GOV.UK for UK bank holidays, the Cabinet Office list in Japan, the State Council annual notice in China.
2. The official gazette or labour ministry publication when no single list exists.
3. Two independent public compilations, checked against each other, only when the first two routes fail.

How a year gets verified

Each country's list is entered from the official source, then compared entry by entry against a second compilation. Mismatches are resolved in favour of the official source and logged. In the 2026 pass, the recurring mismatch types were substitute-day handling in the UK, observed-day handling in the US, and tentative Islamic dates in Saudi Arabia, which stay marked tentative until the moon-sighting announcement.

Known limits

• Islamic holidays shift by a day or two with moon sighting. We publish the projected date and flag it.
• Governments announce changes late. China typically publishes the next year's arrangement in the autumn.
• Regional holidays are out of scope for v1 and are not mixed into national lists.

Corrections go through the contact form. A correction that cites an official source gets applied first.