Time Zone Converter
When a 10:00 London meeting hits 06:00 EST in winter, 05:00 EST in summer, 19:00 in Tokyo and 21:00 in Sydney, keeping the whole team on one clock is non-trivial. This converter takes a date, a source timezone and any destination timezones, and reports each local time — with daylight-saving transitions handled automatically via the IANA timezone database, so March and November adjustments just work.
How conversions are computed
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1
Pick source timezone
Any IANA zone — Europe/London, America/New_York, Asia/Tokyo.
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2
Enter a date and time
The moment in the source zone you want to convert.
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3
Pick destination zones
One or several.
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4
See the local times
Each destination shows its local date and time, with UTC offset and DST flag.
Common business overlaps
| Route | Winter (UTC) | Summer (UTC) |
|---|---|---|
| London → New York | -5 hours | -5 hours |
| New York → LA | -3 hours | -3 hours |
| London → Tokyo | +9 hours | +8 hours |
| New York → Tokyo | +14 hours | +13 hours |
| Berlin → Sydney | +9 hours | +8-10 hours |
Daylight saving makes the summer-winter gap shift because different countries transition on different days (US: 2nd Sun March; EU: last Sun March; Australia: 1st Sun April).
Why IANA timezones matter
“PST” or “EST” are ambiguous — they don’t say whether DST is in effect. IANA names like America/Los_Angeles always resolve correctly because they include DST rules for every year. Always use IANA names for scheduling across regions.
Fixed vs DST-observing zones
- No DST: Arizona, Hawaii, Japan, China, India, most of the Middle East.
- Observes DST: Most of Europe, US and Canada, Australia (varies by state), parts of South America.
- Southern Hemisphere flip: Australia and New Zealand DST is opposite to the Northern Hemisphere, so “summer time” relative to each is correct, but the calendar dates differ.
The “fall back” ambiguous hour
On DST end night, clocks go backward — meaning 01:30 happens twice (once before, once after the shift). For scheduled meetings, avoid the 01:00-03:00 window on transition nights. Otherwise, always specify “before DST end” or “after DST end” if ambiguity matters.
The “spring forward” missing hour
DST start: clocks jump forward, so 02:30 simply doesn’t exist that day. If you try to schedule a meeting at 02:30 local on spring-forward Sunday, many calendar apps silently shift it to 03:30 or 01:30. Avoid this window too.
Frequently Asked Questions
Most likely the reminder was saved with a fixed UTC offset (e.g. “UTC-5”) instead of an IANA timezone. When DST transitions, the offset changes but the fixed setting doesn’t. Save events with the IANA zone name to fix this permanently.
Yes. A 23:00 London time converts to 18:00 New York same day, but 09:00 Tokyo next day from London. The date rollover is handled automatically.
For practical purposes, none — both are zero-offset time. UTC is defined by atomic clocks with leap seconds; GMT is the historical British mean solar time. In software, always use UTC; GMT is legacy.
No. The browser ships with the IANA database and all conversion happens locally.
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