Timezone Converter (compare time across multiple zones)
Pick a source timezone and date/time, then add as many target timezones as you need. Each target shows the equivalent local time with timezone abbreviation.
How it works
How timezone conversion works
Every moment in time is a single point — Tuesday 9am in Tokyo is the same moment as Monday 5pm in San Francisco. Timezone conversion just relabels that single moment with the local clock-face time of each zone. Daylight saving time complicates this — between March and November in the US, Eastern time is UTC-4 (EDT); the rest of the year it's UTC-5 (EST). The browser's Intl.DateTimeFormat handles all this correctly when you pass an IANA timezone name like 'America/New_York'.
We use IANA names (like 'Asia/Tokyo' or 'Europe/London') because they're unambiguous and follow each location's DST rules historically. 'JST' or 'GMT' are abbreviations that may collide; IANA names won't.
Common scheduling pitfalls
DST transitions: 'next Tuesday at 9am EST' is ambiguous in March or November because the rules change. Always say 'New York time' or send a calendar invite — Outlook, Google Calendar, and Slack all handle conversion correctly when both sides specify their zone.
Half-hour offsets: India is UTC+5:30, Newfoundland is UTC-3:30, parts of Australia are UTC+9:30 or +10:30. If your meeting math is in 'whole hours', you'll be 30 minutes off for these regions.
Cross-date-line jumps: Tokyo to San Francisco is the next-day vs same-day depending on direction. The calendar shows it correctly, but the human assumption can be wrong.
Useful patterns
International standup: Pick a source zone (often UTC) and the team's home timezones. Set the meeting time and verify no one is asked to attend at 3am.
Product launch: Pick the launch zone and add the major markets. Useful for verifying the marketing email arrives at a sensible local hour.
Travel planning: Pick your departure zone and add destination zone(s) to find the local arrival time without manual math.
Frequently asked questions
›Does it handle DST?
Yes — IANA timezone data includes DST rules for each location. The browser's Intl API handles past, present, and (where known) future transitions.
›What's the difference between EST and ET?
EST is fixed at UTC-5. ET (Eastern Time) is EST in winter and EDT in summer — it tracks DST. We use IANA names like 'America/New_York' which automatically pick EST or EDT based on the date.
›Can I convert between two specific cities?
Yes. Set one as the source and add the other as a target. The displayed time is the source moment expressed in target's local clock.
›Why do some zones have :30 offsets?
Historical decisions. India, Iran, Afghanistan, Newfoundland, parts of Australia all use 30-minute or 45-minute offsets from UTC. The calculator handles these correctly.
›Does this work for past dates?
Yes, including DST boundaries that may have been different historically. IANA data covers most location histories from 1970 onward.
›What about Antarctica or Hawaii?
The IANA list includes them. Add 'Pacific/Honolulu' or 'Antarctica/McMurdo' from the dropdown if needed.
›Is the data sent anywhere?
No. The browser's Intl APIs handle everything locally.
›Can I save my list of timezones?
Not yet. Refreshing the page resets the list. We may add local-storage persistence later.
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