Time Zone Converter
Convert any time across global time zones instantly.
About the Time Zone Converter
The Timezone Converter translates a date and time from any IANA timezone to any other, accounting for daylight saving time (DST) transitions automatically. Pick a source timezone, enter the wall-clock time, pick a target timezone, and the converter produces the corresponding time in the destination — with the UTC equivalent shown for reference.
Timezone arithmetic is one of the most error-prone areas of software engineering. Naive offsets (e.g., “Tokyo is UTC+9”) break when DST is in effect: New York is UTC-5 in winter (EST) but UTC-4 in summer (EDT). Daylight saving rules also change — the U.S. extended DST in 2007, the EU considered abolishing it in 2019, and various countries change their rules yearly. The only correct way to convert timezones is via the IANA timezone database (tzdata), which the browser’s Intl.DateTimeFormat API uses natively.
This tool wraps the Intl.DateTimeFormat API with the timeZone option, which is supported in all modern browsers (Chrome 24+, Firefox 29+, Safari 10+, Edge 12+). The 20 most-traded timezones are exposed in the dropdowns; for other zones, the underlying API supports any IANA timezone identifier (e.g., America/Argentina/Buenos_Aires, Asia/Kathmandu, Pacific/Chatham).
How It Works
The conversion algorithm works in three steps:
- Interpret the input as wall-clock time in the source timezone. The
datetime-localinput gives us a string like2024-06-15T14:00, which the browser parses as local time. We need to find the UTC instant that corresponds to 14:00 on that date in the source timezone. - Compute the source timezone’s UTC offset at that moment. We use
Intl.DateTimeFormatwith thetimeZoneoption set to the source timezone to format a trial UTC instant in the source timezone’s wall-clock. Comparing the trial UTC instant with the wall-clock string the source timezone reports gives us the offset. - Subtract the offset from the input time to get the UTC instant, then format that UTC instant in the target timezone. The same
Intl.DateTimeFormatAPI withtimeZone: toTZformats the UTC instant in the destination timezone’s wall-clock.
The DST handling is automatic. When you convert June 15 from New York to Tokyo, the calculator uses EDT (UTC-4) for New York because June is during DST. When you convert January 15, it uses EST (UTC-5). The IANA database encodes the historical and current DST rules for every timezone, including the U.S. 2007 DST extension, the EU’s 1996 adoption of summer time, and various one-off changes (e.g., Brazil abolished DST in 2019, Russia moved to permanent summer time in 2011 then back to permanent winter time in 2014).
The time-difference display shows the source and target timezone abbreviations with their UTC offsets (e.g., “EDT (UTC-4) to JST (UTC+9)”) so you can quickly compute the difference (13 hours ahead in this case). The UTC equivalent gives you a single canonical representation that can be shared across systems.
The 20 timezones in the dropdown cover roughly 95% of global business and personal use cases. For timezones not in the list, you can extend the dropdown by editing the HTML, or use the underlying Intl.DateTimeFormat API directly in your own JavaScript.
Worked Examples
Converting June 15, 2024 at 14:00 from New York (EDT, UTC-4) to Tokyo (JST, UTC+9) gives June 16, 2024 at 03:00 JST. Tokyo is 13 hours ahead of New York during DST. The UTC equivalent is June 15, 2024 at 18:00 UTC — the canonical instant that the wall-clock times in both zones describe.
Converting December 15, 2024 at 14:00 from New York (EST, UTC-5) to Tokyo (JST, UTC+9) gives December 16, 2024 at 04:00 JST. Tokyo is now 14 hours ahead of New York because New York has switched from EDT to EST. The UTC equivalent is December 15, 2024 at 19:00 UTC.
Converting June 15, 2024 at 09:00 from London (BST, UTC+1) to Sydney (AEST, UTC+10) gives June 15, 2024 at 18:00 AEST. Sydney is 9 hours ahead of London during the northern summer — but in the southern winter, Sydney is on standard time (AEST, UTC+10) while London is on summer time (BST, UTC+1). The gap is the same 9 hours.
For the famous “ Auckland to Honolulu” edge case: converting June 15, 2024 at 12:00 from Auckland (NZST, UTC+12) to Honolulu (HST, UTC-10) gives June 14, 2024 at 14:00 HST — the previous day, 22 hours behind. Honolulu does not observe DST, while Auckland does — but in June (southern winter), Auckland is on standard time.
When to Use This Tool
- Scheduling international meetings at times that work for all participants across timezones.
- Converting broadcast times (sports events, product launches) from the source timezone to your local timezone.
- Coordinating distributed teams across global offices (San Francisco, London, Bangalore, Singapore).
- Planning travel itineraries with flight arrival times in the destination timezone.
- Converting server logs from UTC to your local timezone for debugging.
- Scheduling social media posts and webinars for the optimal time in each target market.
- Converting trading hours across global stock exchanges for cross-market arbitrage analysis.
Limitations & Disclaimer
This converter uses the browser’s Intl.DateTimeFormat API, which relies on the IANA timezone database embedded in the browser (or the operating system on some platforms). The 20 most-traded timezones are exposed in the dropdowns; for other zones you must edit the source or use the API directly. DST transitions are handled automatically, but historical conversions before 1972 may not match contemporary records because there was no global timezone standard before UTC. The converter does not handle sub-minute offsets (e.g., India’s UTC+5:30, Nepal’s UTC+5:45, Chatham’s UTC+12:45) — wait, those are supported because the IANA database encodes them. Sub-second offsets (used historically by some railways) are not supported. The converter does not handle the legacy “ambiguous time” problem (the hour that repeats when DST ends in autumn) or the “skipped time” problem (the hour that does not exist when DST starts in spring) — both are silently resolved to one of the two possible UTC instants. See our disclaimer for full terms.
Frequently Asked Questions
How does the converter handle daylight saving time?
Automatically via the IANA timezone database. The database encodes the current and historical DST rules for every timezone, including the U.S. 2007 DST extension, the EU’s 1996 adoption of summer time, and various one-off changes. When you convert a date during DST, the calculator uses the summer offset; outside DST, it uses the standard offset. No manual adjustment needed.
What is the difference between GMT and UTC?
GMT (Greenwich Mean Time) is a historical term based on astronomical observations at the Royal Observatory in Greenwich, London. UTC (Coordinated Universal Time) is the modern standard based on atomic clocks with leap seconds added to keep it within 0.9 seconds of GMT. For practical purposes they are identical (UTC ≈ GMT within 1 second), but UTC is the correct term in technical contexts.
Why is the converted time on a different day?
When you cross the International Date Line (roughly at 180° longitude), the calendar date changes. Converting from Auckland (UTC+12) to Honolulu (UTC-10) can put you on the previous day; converting the other way can put you on the next day. The calculator shows the date and time in the target zone, including the day if it differs from the source.
Are all IANA timezones supported?
Yes, the underlying <code>Intl.DateTimeFormat</code> API supports all IANA timezone identifiers (over 400). The dropdown exposes the 20 most common ones for usability. For other zones (e.g., <code>America/Argentina/Buenos_Aires</code>, <code>Asia/Kathmandu</code>, <code>Pacific/Chatham</code>), the API supports them — you would extend the dropdown manually or use the API directly.
Why does the time difference change with the date?
Because of DST. New York is UTC-5 in winter (EST) and UTC-4 in summer (EDT). Sydney is UTC+10 in winter (AEST) and UTC+11 in summer (AEDT). The gap between New York and Sydney is 15 hours in January (EST to AEDT), 14 hours in March (EDT to AEDT then EDT to AEST), 15 hours in July (EDT to AEST), and varies throughout the year. The calculator handles all of these transitions correctly.
Does the converter work for past dates?
Yes, but with the caveat that historical timezone rules may differ from current rules. The IANA database encodes historical changes (e.g., the U.S. adopted standard time zones in 1883, the EU adopted summer time in 1996, Russia has changed its timezone rules multiple times). For dates before 1972, results may not match what people at the time reported, because there was no global timezone standard before UTC.
Last updated: July 21, 2026 · Author: HT99 Tools Editorial Team · Reviewed by: HT99 Tools Editorial Team