Time Zone Converter Guide: Convert and Compare Times Worldwide
How time zones and daylight saving really work, plus a fast way to pick a meeting time that works for people in three different countries.
I have booked a call for 3pm and had someone show up at 3am. Once is enough to make you paranoid about time zones forever. If you work with anyone more than a couple of borders away, a Timezone Converter is one of those small tools you end up opening two or three times a day.
The part that trips everyone up
A time zone isn’t a fixed number. It’s a rule that changes twice a year in a lot of places.
Take London and New York. Most of the year they’re five hours apart. But the US and the UK don’t switch to daylight saving on the same weekend — the US moves its clocks on the second Sunday of March, the EU and UK on the last Sunday of March. For those two or three weeks in between, London and New York are only four hours apart. People miss calls every single March because of that gap, and they blame themselves instead of the calendar.
This is why “just add five hours” fails. You have to convert for the actual date, not a rule of thumb. The converter does exactly that: it asks your browser’s time zone database what the offset was on that specific day, DST and all.
Offsets are weirder than you think
Whole hours are the common case, not the rule.
- India runs on UTC+05:30 — half an hour off the grid, for the whole country.
- Nepal goes further with UTC+05:45. Fifteen minutes.
- Cross the globe and the spread is bigger than a day. Kiribati’s Line Islands sit at UTC+14, while Baker Island is UTC−12. Same moment, 26 hours of clock difference.
That last one is why a converter sometimes shows a city on tomorrow’s date, or still on yesterday’s. When you pin a time in one zone, the tool flags any city that has crossed midnight relative to your source with a small “next day” or “previous day” badge. It’s the detail that stops you from booking Tuesday’s meeting on Wednesday in Sydney.
A method for scheduling across three zones
Here’s what actually works when you’re juggling, say, San Francisco, Berlin, and Singapore.
Start from the person with the least flexible day — usually whoever is furthest ahead. Nobody in Singapore wants a 11pm call. Find the window that’s still daytime there, then check what it maps to for everyone else. You’re not looking for perfect; you’re looking for “awake and not resentful.” Mid-morning in California often lands in the early evening in Europe and late evening in Asia, which is about as fair as it gets for that spread.
Set the source zone to whichever city you’re anchoring on, type the candidate time, and read the other cards. Two minutes, no mental arithmetic, no March disasters.
Why it runs in your browser
Every modern browser ships a full copy of the IANA time zone database — the same data Linux and macOS use. That means the conversion happens locally, through the built-in Intl API. Nothing you type leaves the page, and the tool keeps working on a plane with the Wi-Fi off.
Your list of cities and your 12- or 24-hour preference are saved in your browser too, so the zones you check every morning are still there tomorrow.
Add the cities you care about to the Timezone Converter and keep it open in a tab — the clocks tick in real time, and the next 3am mix-up won’t be yours.