Time Zone Converter
Current Time
--
--
UTC offset: --
Converted Time
--
--
UTC offset: --
Time Difference
--
How Time Zone Conversion Works
The world is divided into time zones, each defined as an offset from Coordinated Universal Time (UTC). UTC is the successor to Greenwich Mean Time (GMT) and is maintained by a network of over 400 atomic clocks at laboratories worldwide, coordinated by the International Bureau of Weights and Measures (BIPM) in Paris. According to the IANA (Internet Assigned Numbers Authority), which maintains the authoritative time zone database used by virtually all computer systems, there are over 400 named time zone regions, each with its own rules for UTC offset and daylight saving time transitions.
Daylight Saving Time (DST) adds significant complexity to time zone conversions. When DST is active, clocks advance by one hour, changing the UTC offset. Approximately 70 countries observe DST, but they transition on different dates. The US and Canada switch in March and November; the EU switches in late March and late October; southern hemisphere countries like Australia and New Zealand switch in opposite months. This means the time difference between two cities can change 2-4 times per year. This converter uses the browser's built-in Intl.DateTimeFormat API with IANA time zone identifiers, automatically handling all DST transitions past, present, and future. For related time tools, see our date difference calculator and working days calculator.
Key Terms
- UTC (Coordinated Universal Time): The global time standard. All time zones are expressed as offsets from UTC (e.g., UTC-5 for US Eastern Standard Time).
- DST (Daylight Saving Time): A seasonal clock adjustment (typically +1 hour in summer) observed by about 70 countries to extend evening daylight.
- IANA Time Zone: A location-based identifier (e.g., "America/New_York") that encodes both the UTC offset and all historical/future DST rules for that region.
- International Date Line: The boundary in the Pacific Ocean where the calendar date changes, roughly following the 180-degree meridian.
- Offset: The number of hours (and sometimes minutes) added to or subtracted from UTC to get local time. Ranges from UTC-12 to UTC+14.
Major City Time Zone Offsets
| City | Standard Offset | DST Offset | DST Period |
|---|---|---|---|
| New York | UTC-5 (EST) | UTC-4 (EDT) | Mar-Nov |
| London | UTC+0 (GMT) | UTC+1 (BST) | Mar-Oct |
| Paris / Berlin | UTC+1 (CET) | UTC+2 (CEST) | Mar-Oct |
| Dubai | UTC+4 (GST) | No DST | -- |
| Mumbai | UTC+5:30 (IST) | No DST | -- |
| Tokyo | UTC+9 (JST) | No DST | -- |
| Sydney | UTC+10 (AEST) | UTC+11 (AEDT) | Oct-Apr |
| Auckland | UTC+12 (NZST) | UTC+13 (NZDT) | Sep-Apr |
Practical Examples
Example 1 -- US to Europe meeting: Schedule a call between New York (ET) and London (GMT/BST). During US summer: New York is UTC-4, London is UTC+1. Difference = 5 hours. A 10:00 AM New York call is 3:00 PM London. During winter: New York is UTC-5, London is UTC+0. Difference = 5 hours (same, because both regions change DST within a few weeks of each other).
Example 2 -- Cross-Pacific collaboration: Tokyo (UTC+9, no DST) and San Francisco (UTC-8 standard, UTC-7 DST). During US summer: difference = 16 hours. A 5:00 PM Monday meeting in San Francisco is 9:00 AM Tuesday in Tokyo. Use our age calculator for date-based computations.
Example 3 -- India to multiple zones: Mumbai (UTC+5:30, no DST) to London and New York. Mumbai to London: 5.5 hours ahead (standard) or 4.5 hours (BST). Mumbai to New York: 10.5 hours ahead (EST) or 9.5 hours (EDT). The half-hour offset makes mental arithmetic trickier.
Tips for Working Across Time Zones
- Always specify the time zone: When scheduling, include the time zone abbreviation (e.g., "3:00 PM EST" not just "3:00 PM"). Ambiguous times cause missed meetings.
- Use UTC for global coordination: For teams spanning many zones, expressing times in UTC eliminates confusion. "Meeting at 14:00 UTC" is unambiguous worldwide.
- Watch for DST transition weeks: The 2-3 weeks between US and EU DST changes create unusual offset differences. Double-check conversion during March and November.
- Account for the International Date Line: When converting between Asia/Oceania and the Americas, the date may change. A Friday evening in Los Angeles can be Saturday morning in Tokyo.
- Use calendar tools with time zone support: Google Calendar, Outlook, and Apple Calendar all handle time zone conversion automatically when you set the correct zones for events.
Frequently Asked Questions
What is UTC and how do time zones work?
UTC (Coordinated Universal Time) is the primary time standard used worldwide, maintained by a network of over 400 atomic clocks. Time zones are defined as offsets from UTC, ranging from UTC-12 (Baker Island) to UTC+14 (Line Islands, Kiribati). Most time zones are whole-hour offsets, but some use half-hour or quarter-hour offsets: India uses UTC+5:30, Iran uses UTC+3:30, Nepal uses UTC+5:45, and parts of Australia use UTC+9:30. The time zone system was formalized in 1884 at the International Meridian Conference in Washington, D.C., which established Greenwich, England as the prime meridian (0 degrees longitude).
How does daylight saving time affect time zones?
DST shifts clocks forward by one hour in spring and back in fall, temporarily changing a region's UTC offset. For example, New York is UTC-5 in winter (EST) and UTC-4 in summer (EDT). Not all countries observe DST: most of Africa, Asia, and South America do not. Countries that do observe DST change on different dates -- the US changes in March and November, while the EU changes in late March and late October. This means the time difference between two cities can change 2-4 times per year. This converter uses the browser's Intl.DateTimeFormat API with IANA time zone data, which automatically handles all DST transitions.
Why do some countries have unusual time zone offsets?
Some countries choose non-standard offsets to keep the entire country on a single time zone or to better align noon with solar noon for their geographic location. India uses UTC+5:30 because the country spans from UTC+5 to UTC+6 and the half-hour offset splits the difference. Nepal uses UTC+5:45 to distinguish itself from India. The Chatham Islands (New Zealand) use UTC+12:45. China uses a single time zone (UTC+8) despite spanning five geographic time zones, meaning sunrise in western China occurs as late as 10:00 AM during winter months.
How many time zones are there in the world?
There are 38 distinct UTC offsets currently in use worldwide, from UTC-12 to UTC+14. However, the IANA time zone database (used by computers) contains over 400 time zone identifiers because many regions share the same offset but have different DST rules or historical changes. The United States spans six time zones (Eastern, Central, Mountain, Pacific, Alaska, Hawaii-Aleutian), while Russia spans eleven time zones (from UTC+2 to UTC+12). France holds the record for the most time zones of any country (12), due to its overseas territories in the Pacific, Indian Ocean, Caribbean, and South America.
What is the International Date Line?
The International Date Line (IDL) is an imaginary line roughly following the 180-degree meridian in the Pacific Ocean, where the calendar date changes. Crossing the line westward advances the date by one day; crossing eastward moves it back one day. The line is not straight -- it zigzags to avoid splitting countries and island groups into different dates. Kiribati moved its portion of the line eastward in 1995 so the entire country would be on the same date, creating the UTC+14 time zone and making it the first place to experience each new day.
How do I schedule meetings across multiple time zones?
To find overlapping business hours across time zones, identify the earliest acceptable time in the easternmost zone and the latest in the westernmost zone. For US coast-to-coast meetings (ET and PT), the 12:00-5:00 PM ET window (9:00 AM-2:00 PM PT) works best. For US-Europe collaboration, 8:00-11:00 AM ET (1:00-4:00 PM London, 2:00-5:00 PM Paris) is optimal. For US-Asia meetings, early morning or late afternoon are typically necessary due to the 13-17 hour gap. Use our date difference calculator and working days calculator for scheduling across dates.