Time zones define how local clocks relate to UTC (Coordinated Universal Time), the global time standard. The converter above uses IANA time zone identifiers — names like America/New_York and Asia/Tokyo — which include every historical and current daylight saving time (DST) rule automatically.
How the conversion works
The converter translates your chosen date and time into a UTC instant, then re-expresses that instant in the target time zone:
UTC = local time − UTC offset (accounting for DST)
target local time = UTC + target UTC offset (accounting for DST)
The UTC offset changes twice a year in zones that observe daylight saving time. Because the converter uses the IANA database (via your browser's Intl.DateTimeFormat API), it applies the correct offset for the specific date and zone you enter — not a static offset.
Practical examples
Example 1 — New York to London meeting
A meeting is scheduled for 10:00 AM Eastern Time (ET) on a weekday in March (when US DST is active but UK has not yet switched). Eastern Time is UTC−5 during standard time and UTC−4 during daylight saving time.
During US DST (March–November): 10:00 AM ET = UTC−4 → 2:00 PM UTC → 2:00 PM London (GMT)
Example 2 — San Francisco to Tokyo
5:00 PM Pacific Standard Time (PST = UTC−8) on a winter weekday:
5:00 PM PST → 1:00 AM UTC → 10:00 AM Tokyo Standard Time (JST = UTC+9, next day)
Example 3 — Scheduling across the International Date Line
Noon in Los Angeles (PST, UTC−8) is the following day at 5:00 AM in Sydney (AEDT, UTC+11) during Australian summer. The converter handles date-line crossings automatically.
Common mistakes
Using a fixed offset instead of a named zone. Typing "UTC+1" ignores DST — Central European Time is UTC+1 in winter and UTC+2 in summer. Always select the named zone (e.g. Europe/Paris) so DST is applied correctly.
Confusing GMT and UTC. GMT (Greenwich Mean Time) is a time zone; UTC is a time standard. The UK observes GMT in winter (UTC+0) and BST (British Summer Time, UTC+1) in summer. Select Europe/London rather than assuming "GMT" means UTC+0 year-round.
Assuming all zones are whole-hour offsets. India (IST) is UTC+5:30, Nepal (NPT) is UTC+5:45, and Iran (IRST) is UTC+3:30. The converter handles half and quarter-hour offsets correctly.
International and regional variations
| Region | Standard offset | DST offset | DST observed? |
|---|---|---|---|
| Eastern US (ET) | UTC−5 | UTC−4 | Yes (Mar–Nov) |
| Central Europe (CET) | UTC+1 | UTC+2 | Yes (Mar–Oct) |
| India (IST) | UTC+5:30 | — | No |
| Japan (JST) | UTC+9 | — | No |
| Australia Eastern (AEST/AEDT) | UTC+10 | UTC+11 | Yes (Oct–Apr) |
| China (CST) | UTC+8 | — | No |
Quick reference — UTC offsets for major cities
| City | IANA zone | Standard | Summer (DST) |
|---|---|---|---|
| New York | America/New_York | UTC−5 | UTC−4 |
| Chicago | America/Chicago | UTC−6 | UTC−5 |
| Los Angeles | America/Los_Angeles | UTC−8 | UTC−7 |
| London | Europe/London | UTC+0 | UTC+1 |
| Paris / Berlin | Europe/Paris | UTC+1 | UTC+2 |
| Dubai | Asia/Dubai | UTC+4 | UTC+4 |
| Mumbai | Asia/Kolkata | UTC+5:30 | UTC+5:30 |
| Singapore | Asia/Singapore | UTC+8 | UTC+8 |
| Tokyo | Asia/Tokyo | UTC+9 | UTC+9 |
| Sydney | Australia/Sydney | UTC+10 | UTC+11 |