Time across history

Questions

FAQ

How far back does this work?

As far back as the IANA database has explicit rules — generally to around 1900 for Europe and the Americas, earlier for some zones. Before that, the database falls back to LMT (Local Mean Time), which is solar time at the longitude of the city's reference meridian. The result is still a defensible historical answer, just less politically grounded.

Does it handle one-off historical changes correctly?

Yes — the IANA database encodes every documented policy change. Famous examples: Samoa skipping December 30, 2011 to jump the international date line; the UK's year-round DST experiment 1968-1971; Newfoundland adopting standard time at +03:30:30 from 1935 to 1963. Pick any of these dates and you'll see the correct offset.

Why doesn't it handle dates before 1582?

Dates before October 15, 1582 use the proleptic Gregorian calendar — that is, we extend Gregorian dates backwards even though they weren't the calendar in use. Many countries kept Julian dates well past 1582 (Russia until 1918, Greece until 1923). For pre-Gregorian historical research, you'd need a Julian-calendar tool, not this one.

Are pre-1970 results dependable for legal or scientific use?

For most jurisdictions: yes, modulo LMT. The IANA maintainers cite published legal sources and scientific references for every zone change. For absolute precision in legal or astronomical contexts, cross-check against the maintainer's notes in the IANA tz-link database — links from each transition row point to the underlying rule.