Timezone FAQ
Common questions about time zones, UTC, Daylight Saving Time, and scheduling across timezones.
What is a time zone?
A time zone is a region of the world that uses the same standard time. Time zones are defined by their offset from Coordinated Universal Time (UTC). Most time zones are offset by whole hours, though some — like India (UTC+5:30) and Nepal (UTC+5:45) — use half- or quarter-hour offsets.
What does UTC mean?
UTC stands for Coordinated Universal Time. It is the primary time standard used worldwide and the basis for all time zone offsets. UTC replaced GMT (Greenwich Mean Time) as the global reference in 1960. When you see 'UTC+5' or 'UTC-8', those numbers represent how many hours ahead or behind UTC the local time is.
What is the difference between UTC and GMT?
GMT (Greenwich Mean Time) and UTC refer to the same time — the mean solar time at the Royal Observatory in Greenwich, London. In practice, UTC is the scientific standard used for computing and telecommunications, while GMT is a time zone used by some countries (mainly the UK in winter). For everyday conversion purposes, they are interchangeable.
What is Daylight Saving Time (DST)?
Daylight Saving Time (DST) is the practice of setting clocks forward by 1 hour during spring and summer months to extend evening daylight. Clocks are then moved back in autumn. DST is observed by most of Europe, North America, and parts of the Southern Hemisphere — but not by countries like Japan, China, India, or most of Africa and Southeast Asia.
When does Daylight Saving Time start and end?
DST dates vary by region. In the United States and Canada, clocks spring forward on the second Sunday in March and fall back on the first Sunday in November. In Europe, clocks change on the last Sunday in March and the last Sunday in October. Australia (where summer is opposite) observes DST from October to April. whattimewillitbein.com automatically accounts for these transitions so your conversions are always correct.
Which countries do not observe Daylight Saving Time?
Most of Asia, Africa, and Southeast Asia do not observe DST. Notable examples include Japan, China, India, South Korea, Singapore, the UAE, Saudi Arabia, Egypt, Nigeria, and Kenya. Within countries that observe DST, some regions may be exempt — for example, Arizona (US) does not observe DST while the rest of the continental US does.
What is the time difference between EST and PST?
Eastern Standard Time (EST, UTC-5) is 3 hours ahead of Pacific Standard Time (PST, UTC-8). During summer, both US coasts observe daylight time — EDT is UTC-4 and PDT is UTC-7 — and the 3-hour difference remains the same.
What is the time difference between GMT and EST?
GMT (UTC+0) is 5 hours ahead of Eastern Standard Time (EST, UTC-5). During US Daylight Saving Time (EDT, UTC-4), the difference shrinks to 4 hours. During UK Summer Time (BST, UTC+1), it becomes 6 hours. Use the calculator to check the current live difference.
How do I convert time between two cities?
Enter your source city and the time you want to convert on whattimewillitbein.com. The calculator shows you the converted time in the destination city, automatically accounting for each city's current UTC offset and any active Daylight Saving Time adjustments. You can also share a permanent link to the conversion.
What is the best time to schedule a meeting between the US and Europe?
The best overlap for US–Europe calls is typically 9–10 AM Eastern / 3–4 PM Central European Time (CET). This gives both parties a reasonable working hour. During European Summer Time (CEST), the overlap shifts by 1 hour. Use the business overlap tool on any US-to-Europe city pair page to find the exact current window.
What is the best time to schedule a meeting between the US and Asia?
Scheduling between the US and Asia is challenging due to a 12–16 hour difference. Early morning US Eastern time (6–8 AM) aligns with end-of-day Asia time (7–9 PM). For teams in Los Angeles and Tokyo, a 6–8 AM PST window works best. There is rarely a true business-hours overlap — one team will always need to meet outside standard hours.
What does +5:30 mean in a time zone?
UTC+5:30 means the local time is 5 hours and 30 minutes ahead of Coordinated Universal Time. India Standard Time (IST) uses UTC+5:30. Half-hour offsets exist because historical timekeeping was tied to solar noon at a country's geographic center, and some countries chose to preserve that rather than round to the nearest full hour.
Why do time zones change for the same city across the year?
When a country observes Daylight Saving Time, the UTC offset of all cities in that zone shifts by 1 hour during summer. For example, New York is UTC-5 (EST) in winter and UTC-4 (EDT) in summer. This is why the time difference between, say, New York and London changes from 5 hours to 4 hours depending on the season — because the UK and US do not change clocks on the same day.
How many time zones are there?
There are 24 primary time zones based on full-hour UTC offsets, but including half-hour and quarter-hour offsets, there are over 40 distinct time zones in use worldwide. Some countries like Russia and the US span multiple zones. China uses a single zone (UTC+8) for the entire country despite its geographic span.
Is whattimewillitbein.com free to use?
Yes. whattimewillitbein.com is completely free with no account required. All features — timezone conversion, future time calculation, shareable links, and DST-aware results — are available to all users at no cost.
Ready to convert a specific time?
Open the timezone calculator →