Article — Time Zones Converter
Time zones converter — convert across world cities and UTC
- What is a time zones converter?
- UTC — the universal reference time
- Daylight saving time in the time zones converter
- Non-hour time zones — India, Nepal, Australia
- IANA database and the time zones converter
- Time zones converter for global meetings
- Common time zones conversion mistakes
- Brief history of time zones
A time zones converter takes a wall-clock date and time in one zone and outputs the same instant in any other zone in the world. The math is straightforward — subtract the source UTC offset, then add the target offset — but real-world quirks make it hard: daylight saving time (DST), non-hour offsets (India +5:30, Nepal +5:45), historical rule changes, and the international date line.
Most global meeting platforms (Zoom, Google Calendar, Microsoft Teams) handle conversion internally using the IANA time-zone database. The converter on this page uses the same database through the browser's Intl API, so DST and historic offsets are handled correctly for any date you pick.
What is a time zones converter?
A time zones converter answers the question "If a meeting is at 3 PM in New York, what time is it in Tokyo?" It does this by treating every wall-clock time as relative to UTC (Coordinated Universal Time). The conversion is: target_local = source_local − source_offset + target_offset, where offsets vary by location and date (because of DST).
UTC — the universal reference time
UTC (Coordinated Universal Time) is the global time standard. It is based on atomic clocks at the BIPM in Paris, with occasional leap seconds inserted to keep it within 0.9 s of mean solar time at Greenwich. UTC has no DST and never changes for political reasons — it is the bedrock of GPS, internet time servers, aviation, and the global financial system.
Every local time can be written as UTC ± an offset. Tokyo is UTC+9, New York is UTC-5 (EST) or UTC-4 (EDT during DST). When two parties agree on a UTC timestamp, there is no ambiguity. The IANA tz database tells the time zones converter exactly which offset applies for any date and zone combination.
UTC and GMT are different in theory but identical in practice. GMT (Greenwich Mean Time) is an astronomical scale; UTC is atomic. They differ by less than 0.9 s at any moment — far below practical relevance. The UK Met Office and BBC use both interchangeably.
Daylight saving time in the time zones converter
DST shifts the local clock forward by one hour for the summer half of the year, then back in autumn. The exact dates differ by country:
- USA and Canada = 2nd Sunday March to 1st Sunday November
- EU and UK = last Sunday March to last Sunday October
- Australia (south) = 1st Sunday October to 1st Sunday April (Southern Hemisphere)
- New Zealand = last Sunday September to 1st Sunday April
- No DST = Russia (since 2014), Turkey (since 2016), Mexico (since 2022), Brazil (since 2019), Japan, China, India, most of Africa
The 2-3 week window each March when US DST has started but EU DST has not creates a temporary offset shift. During this gap, London is 4 hours ahead of New York instead of the usual 5. A time zones converter that does not handle DST correctly will be off by 1 hour for that whole window.
Non-hour time zones — India, Nepal, Australia
Most zones are whole hours offset from UTC, but several use 30- or 45-minute offsets. India (UTC+5:30) is the largest, covering 1.4 billion people. Nepal (UTC+5:45) is the only national zone with a 45-minute offset. South Australia (UTC+9:30 standard, +10:30 DST), Newfoundland (UTC-3:30), and Iran (UTC+3:30) round out the major examples.
Los Angeles UTC-8 / -7 New York UTC-5 / -4London UTC+0 / +1 Berlin UTC+1 / +2India UTC+5:30 Tokyo UTC+9Sydney UTC+10 / +11 Auckland UTC+12 / +13IANA database and the time zones converter
The IANA Time Zone Database (also called tzdata or the Olson database) tracks every zone and DST rule change since 1970. Names follow the pattern "Area/City" — America/New_York, Europe/Berlin, Asia/Kolkata. The database is updated several times a year as countries change rules. macOS, Linux, Android, and all major server platforms include it; Windows uses a parallel database with the same content.
This time zones converter calls the browser's Intl.DateTimeFormat API, which reads the IANA tz database compiled into the JavaScript engine (V8 on Chrome, SpiderMonkey on Firefox, JavaScriptCore on Safari). The result: full historical and future DST accuracy, no separate library needed.
Time zones converter for global meetings
When scheduling a meeting across many zones, three practical rules help. First, pick a UTC anchor — write the meeting time in UTC so attendees can convert with confidence. Second, watch for date rollovers — a 9 AM Monday Pacific meeting is 4 AM Tuesday in Sydney. Third, avoid mid-DST-switch dates if you can; the 2-3 weeks each March and October when US and EU DST schedules diverge are particularly error-prone.
To run a meeting across the Asia-Pacific region, use Singapore or Hong Kong (UTC+8) as the anchor: it overlaps with Australian, Indian, and Japanese business hours. For US-Europe meetings, 14:00 UTC (10 AM ET, 3 PM CET) is the canonical "global" slot.
Common time zones conversion mistakes
Picking the wrong zone abbreviation (CST = Central US, China, or Cuba), forgetting DST, or assuming all India shares one zone (it does, unlike Russia or China). Always use IANA names ("Asia/Kolkata") rather than three-letter codes.
The hour-versus-minute offset confusion (writing 5.30 hours instead of 5h30min for India) is a frequent spreadsheet error. The international date line tricks: someone in Auckland (UTC+13 during DST) can be on Tuesday while someone in Honolulu (UTC-10) is still on Monday — a 23-hour gap that crosses the date line.
Brief history of time zones
Before 1883, every city used local solar time. Trains running cross-country published schedules with dozens of different time references. Sandford Fleming, a Scottish-Canadian engineer, proposed a global system of 24 hour-wide zones in 1879. On 18 November 1883, US and Canadian railroads adopted four zones (Eastern, Central, Mountain, Pacific). The International Meridian Conference in 1884 made Greenwich the prime meridian and laid the foundation for UTC's predecessor, Greenwich Mean Time. The time zones converter you use today is the direct descendant of these 19th-century decisions.
Leap seconds add a final wrinkle. UTC has had 27 leap seconds inserted since 1972 to keep it aligned with Earth's slowing rotation. The international community voted in 2022 to abolish leap seconds by 2035 — after that, UTC will drift slowly away from solar time, but neither computers nor time zones converters will need special handling.