What a timezone converter is for
Coordinating times across countries is harder than it looks. A remote meeting with a team spread across Buenos Aires, Madrid and Mexico City involves three different clocks, and two of those cities do not even keep the same gap all year. If you work with clients on another continent, have family scattered around the world, are planning a trip with layovers, or do not want to miss a stream, a product launch or a sports final announced "at 20:00 CET", you need to translate that time into your own without slipping up.
This converter interprets the time you enter in the source timezone you choose and shows it in several cities at once, flagging whether the result lands on the next or the previous day. The classic mistake — forgetting about daylight saving — cannot happen here: the conversion uses the browser's own timezone database, which already knows which rule applies in each city on each date of the year.
How the conversion works
Every timezone is identified by an IANA name in the Region/City format (for example, America/Argentina/Buenos_Aires or Europe/Madrid). That name does not store a fixed offset: it stores the full rule history for that region, including daylight saving changes. The tool converts the time you enter into a universal instant (UTC) using the source zone's offset on that exact date, then projects that instant into every destination city. That is why the result is correct in January and in July alike, even though the gap between two cities changes during the year.
Reference table: timezones of 16 major cities
Offsets are expressed relative to UTC. For cities with daylight saving time, the "Summer UTC" column applies during their local summer (which in the southern hemisphere runs from the end of one year into the start of the next).
| City | IANA zone | Standard UTC | Summer UTC | Daylight saving? |
|---|---|---|---|---|
| Buenos Aires | America/Argentina/Buenos_Aires | −3 | −3 | No (unchanged since 2009) |
| Montevideo | America/Montevideo | −3 | −3 | No (dropped it in 2015) |
| São Paulo | America/Sao_Paulo | −3 | −3 | No (abolished in 2019) |
| Santiago | America/Santiago | −4 | −3 | Yes (September to April) |
| Bogotá | America/Bogota | −5 | −5 | No |
| Lima | America/Lima | −5 | −5 | No |
| Mexico City | America/Mexico_City | −6 | −6 | No (abolished in 2022) |
| New York | America/New_York | −5 | −4 | Yes (March to November) |
| Los Angeles | America/Los_Angeles | −8 | −7 | Yes (March to November) |
| London | Europe/London | 0 | +1 | Yes (March to October) |
| Madrid | Europe/Madrid | +1 | +2 | Yes (March to October) |
| Dubai | Asia/Dubai | +4 | +4 | No |
| New Delhi | Asia/Kolkata | +5:30 | +5:30 | No |
| Shanghai | Asia/Shanghai | +8 | +8 | No |
| Tokyo | Asia/Tokyo | +9 | +9 | No |
| Sydney | Australia/Sydney | +10 | +11 | Yes (October to April) |
Tips for scheduling across timezones
- Always propose the time in a single reference zone (or directly in UTC) and let everyone convert it to their own.
- Watch the transition weeks: the United States and Europe do not change their clocks on the same day, so in March and late October the usual gaps shift by one hour for a few days.
- Between hemispheres, daylight saving works in reverse: when Madrid is in summer, Santiago is in winter, and vice versa.
- If the result shows "+1 day", double-check the date as well as the time when you put it on the calendar: it is the most common mistake in meetings with Asia and Oceania.