Time Zone Converter

There are 24 primary time zones based on the division of the Earth into 24 longitudinal segments of 15 degrees each, but the actual number of distinct UTC offsets in use today is 38. This discrepancy arises because several countries and territories have adopted non-standard offsets — such as India's UTC+5:30, Nepal's UTC+5:45, and Iran's UTC+3:30 — and because the International Date Line creates additional zones. Some large countries span many zones: Russia uses 11 time zones, the United States uses 6 (9 including territories), and France, when counting its overseas territories, spans 12 time zones — the most of any country. The IANA Time Zone Database, the authoritative source used by most operating systems and our converter, tracks over 400 distinct timezone identifiers that encode both current offsets and historical changes.

UTC (Coordinated Universal Time) and GMT (Greenwich Mean Time) represent the same time value — both correspond to the time at 0 degrees longitude — but they differ in nature and precision. GMT is a time zone, originally defined by the mean solar time observed at the Royal Observatory in Greenwich, London. UTC is a time standard maintained by a network of over 450 atomic clocks worldwide and is accurate to within a nanosecond per day. The practical difference matters when the UK enters British Summer Time (BST): during BST, UK clocks are at UTC+1, but UTC itself does not change. For everyday purposes, UTC and GMT are interchangeable during UK winter, but for technical, scientific, and aviation applications, UTC is the correct reference because it is not affected by Daylight Saving Time.

Daylight Saving Time (DST) is the practice of advancing clocks by one hour during summer months so that evenings have more daylight and mornings have less. Approximately 70 countries observe DST, affecting about 1.6 billion people. Major observers include the United States, Canada, most of the European Union, parts of Australia, New Zealand, and several South American countries. Notable non-observers include Japan, South Korea, China, India, most of Africa, and most of Southeast Asia. The transition dates vary: the US and Canada switch on the second Sunday of March and the first Sunday of November, while the EU switches on the last Sunday of March and the last Sunday of October. The debate over DST's usefulness continues, with the EU having voted to abolish seasonal clock changes (though implementation has been delayed) and several US states proposing permanent DST.

To convert Eastern Standard Time (EST) to Pacific Standard Time (PST), subtract 3 hours. EST is UTC−5 and PST is UTC−8, so the difference is always 3 hours when both zones are on standard time. For example, 3:00 PM EST = 12:00 PM (noon) PST. During Daylight Saving Time, EST becomes EDT (UTC−4) and PST becomes PDT (UTC−7), but the 3-hour difference remains the same: 3:00 PM EDT = 12:00 PM PDT. The gap changes only in the rare case where one zone has switched to DST but the other hasn't — this can happen briefly during the transition weekends if you are converting between a location that observes DST and one that doesn't (like Arizona, which stays on MST year-round).

South Korea uses Korea Standard Time (KST), which is UTC+9 — the same offset as Japan Standard Time (JST). KST is 14 hours ahead of EST (UTC−5) and 17 hours ahead of PST (UTC−8) during standard time, or 13 and 16 hours ahead during US Daylight Saving Time. South Korea does not observe Daylight Saving Time, so KST remains at UTC+9 year-round. Historically, Korea used different time offsets: under Japanese rule, UTC+9 was imposed in 1912, then South Korea briefly used UTC+8:30 from 1954 to 1961 before reverting to UTC+9. To convert from KST to EST, subtract 14 hours (or 13 hours during EDT). For example, 9:00 AM KST = 7:00 PM EST (previous day).

Non-standard offsets exist because time zone boundaries are political decisions, not purely geographic ones. India adopted UTC+5:30 as a compromise between the solar times of its eastern and western extremes — Kolkata is at approximately UTC+5:53 and Mumbai at UTC+4:51, so UTC+5:30 splits the difference. Nepal chose UTC+5:45 partly to assert its national identity as distinct from India. Iran uses UTC+3:30, which closely matches the solar time at Tehran's longitude (51.4°E ÷ 15 = 3.43 hours east of Greenwich). Afghanistan uses UTC+4:30, the Chatham Islands use UTC+12:45, and the Marquesas Islands use UTC−9:30. These fractional offsets mean the time difference between two locations is not always a whole number of hours — for instance, Mumbai to Kathmandu is only 15 minutes, and Tehran to New Delhi is exactly 2 hours.

DST can shift meeting times by one hour without anyone noticing until it is too late. If you schedule a recurring weekly meeting between New York (Eastern Time) and London (UK time), the time difference changes twice a year. From November to mid-March, New York is on EST (UTC−5) and London is on GMT (UTC+0), so the gap is 5 hours. From mid-March to late March, the US has already sprung forward to EDT (UTC−4) but the UK is still on GMT, so the gap narrows to 4 hours. From late March to late October, both are on summer time (EDT and BST), so the gap returns to 5 hours. In late October, the UK falls back but the US doesn't until early November, creating a 4-hour gap again. The safest approach is to use timezone-aware calendar tools that automatically adjust for DST, or specify meeting times in UTC.

The IANA Time Zone Database (also called tz database, tzdata, or the Olson database after its original creator Arthur David Olson) is the most widely used reference for time zone information in the world. It is maintained by a volunteer community under the Internet Assigned Numbers Authority (IANA) and is updated several times per year to reflect legislative changes. The database uses region/city identifiers like America/New_York, Europe/London, and Asia/Tokyo rather than abbreviations like EST or GMT, because abbreviations are often ambiguous (CST alone could mean US Central, China, or Cuba Standard Time). Every major operating system (Linux, macOS, Windows, Android, iOS), programming language (Python's pytz/zoneinfo, Java's java.time, JavaScript's Intl API), and web browser uses tzdata to convert between time zones. Our converter also relies on this database to ensure accuracy.

To find the best meeting time across multiple time zones, list each participant's local business hours (typically 9 AM–5 PM) and convert them all to a common reference like UTC. Then look for the overlapping window where all participants are within business hours. For two zones with a small gap (3–5 hours), there is usually a comfortable 3–4 hour overlap. For zones separated by 8+ hours, the overlap shrinks to 1–2 hours or disappears entirely, and you may need to ask some participants to flex their hours slightly. Our multi-zone comparison mode visualizes this overlap automatically: add all the relevant time zones, and the tool highlights the hours where everyone's business hours intersect. For extreme cases (e.g., PST and IST, a 13.5-hour gap), consider rotating meeting times weekly or using asynchronous communication instead.

The most common time zone abbreviations used internationally are: UTC (Coordinated Universal Time, UTC+0), GMT (Greenwich Mean Time, UTC+0), EST/EDT (Eastern Standard/Daylight Time, UTC−5/−4), CST/CDT (Central Standard/Daylight Time, UTC−6/−5), MST/MDT (Mountain Standard/Daylight Time, UTC−7/−6), PST/PDT (Pacific Standard/Daylight Time, UTC−8/−7), CET/CEST (Central European Time/Summer Time, UTC+1/+2), EET/EEST (Eastern European Time/Summer Time, UTC+2/+3), IST (India Standard Time, UTC+5:30), JST (Japan Standard Time, UTC+9), KST (Korea Standard Time, UTC+9), CST (China Standard Time, UTC+8), AEST/AEDT (Australian Eastern Standard/Daylight Time, UTC+10/+11), and NZST/NZDT (New Zealand Standard/Daylight Time, UTC+12/+13). Be aware that some abbreviations like CST and IST are ambiguous — CST can refer to US Central, China, or Cuba, and IST can mean India, Ireland, or Israel Standard Time.