Time Zone Converter

1. Enter the reference date and time.
2. Choose the source zone and the target zones.
3. The result shows the converted time, the offset from UTC and the zone abbreviation.

An offset such as minus three hours is a number. A zone such as America/Sao_Paulo is a rule: it defines which offset applies on each date of the year, including the history of changes.

That is why conversion needs the date, not just the time. The same pair of cities can be two, three or four hours apart depending on the month, when one side is on daylight saving time and the other is not.

The zone list comes from your browser, through the time zone database that operating systems keep updated. Legislative changes therefore arrive with system updates.

Zone abbreviations are ambiguous and must not be used to identify a zone. CST can mean US Central Time, China Standard Time or Cuba Standard Time — three completely different offsets.

IST is worse still: it serves India, Ireland and Israel.

That is why the correct identifier is always the region and city name, such as America/Sao_Paulo or Europe/Madrid. The abbreviation is shown for information only, never accepted as input.

Brazil has not observed daylight saving since 2019, while the United States and Europe do — on different dates from each other. That creates weeks of the year when the gap to São Paulo shifts twice.

For a recurring meeting across zones, anchor the time to one side’s zone rather than fixing an offset — that way the meeting follows the change instead of sliding by an hour.

In software, always store the instant in UTC and convert only for display. That practice avoids most date bugs.