Dates and time
Epoch numbers, and the offset that applied on the day.
- Convert a time between time zonesGive it a date, a time and a zone. The same instant appears on every other clock you ask for, with the offset that applied on that date rather than the one that applies today.
- Convert a Unix timestamp to a datePaste an epoch number and read the date, or paste a date and read the number. The size of the value decides whether it is being read as seconds, milliseconds, microseconds or nanoseconds, and the answer says which was chosen.
About these tools
Time arithmetic is deceptive because it looks like counting and is not. Zones shift, offsets change by legislation, and the rules that apply are the ones in force on the date in question rather than the ones in force today. A meeting booked across a daylight boundary is the everyday version of the problem.
These use the zone database the browser already carries, so a date in 1975 gets the offset of 1975. Where an hour genuinely did not happen, or happened twice, the page says so instead of silently picking one and giving you a confident answer to a question with two.