About Whenthere
Whenthere is a small collection of free utilities for two problems that come up constantly and deserve better answers than they usually get: working out what time it is somewhere else, and fixing text that arrived in the wrong shape.
How the time data is calculated
Every offset, daylight saving date, and conversion table on this site is derived from the IANA Time Zone Database, the reference dataset that operating systems and programming languages use to track civil time worldwide. No offset is written by hand anywhere in the codebase.
This matters because time zones change. Mexico abolished daylight saving in 2022 and Brazil did the same in 2019; both changes broke a great deal of published material overnight. Deriving everything from the IANA database means the pages reflect the current rules rather than a snapshot of what was true when someone wrote them.
It also shapes how the pages are written. Saying "London is five hours ahead of New York" is only true for part of the year, because the two places move their clocks on different dates. Instead of picking one number, each page breaks the year into the periods where the gap is genuinely constant and gives the exact dates the clocks change on both sides.
Why everything runs in your browser
The text tools never send your text anywhere. The conversion happens in the page you have open, which means there is no server that could store, log, or read what you paste. This is a deliberate design constraint rather than a feature: a tool that has nothing to send cannot leak anything.
The same constraint keeps the site fast. Pages are static HTML generated ahead of time, so the time zone tables are already in the page when it loads — they do not wait on JavaScript, and they work with scripting turned off entirely.
Corrections
If a page shows something wrong — a bad conversion, an outdated clock-change date, a tool that mangles text it should handle — that is a bug worth fixing rather than a quirk. Time zone rules in particular change with little notice.