Time Zone Converter
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🗽 New York → London
🌴 LA → Tokyo
🏙️ Dubai → Sydney
🌍 World Clock
📅 US ↔ India Meeting
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What Are Time Zones & How Do They Work?
The complete guide to time zones, UTC offsets, and why they exist
Time Zone Basics
Why the World Has 38 Different Times
Time zones exist because the Earth rotates 360° every 24 hours — meaning it rotates 15° per hour. Without time zones, the sun would rise at wildly different clock times in different parts of a country. The solution, formalized in 1884 at the International Meridian Conference, was to divide the world into 24 primary time zones, each approximately 15° of longitude wide, centered on the Prime Meridian (0°) in Greenwich, England.
Each time zone is expressed as an offset from UTC (Coordinated Universal Time) — the global time standard. UTC+0 is the base, with zones ranging from UTC-12 (the far west Pacific) to UTC+14 (the far east Pacific, Kiribati). Confusingly, UTC+14 and UTC-12 can actually exist on the same calendar day simultaneously — meaning the Earth technically spans a 26-hour range at any given moment.
🌍 Key fact: There are 38 distinct UTC offsets in use worldwide — more than 24 because many countries use half-hour (e.g. India UTC+5:30, Iran UTC+3:30) or quarter-hour (Nepal UTC+5:45) offsets. China uses a single time zone despite spanning 5 natural zones.
Modern time zones are defined by the IANA Time Zone Database (also called the Olson database) — a constantly updated record of every time zone, every historical change, and every DST rule in the world. Your phone, computer, and this converter all use this database to handle time zone conversions correctly.
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The Prime Meridian
The Prime Meridian (0° longitude) passes through the Royal Observatory in Greenwich, London. This was chosen as the global reference point in 1884. All time zones are measured east (+) or west (−) of this line.
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How Conversion Works
To convert between time zones: subtract the source UTC offset to get UTC time, then add the target UTC offset. E.g. 9:00 AM EST (UTC-5) → UTC = 2:00 PM → London (UTC+0) = 2:00 PM → IST (UTC+5:30) = 7:30 PM.
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Date Line Crossings
The International Date Line (180° longitude) is where one calendar day becomes the next. Crossing it westward adds a day; eastward subtracts one. This is why a flight from LA to Tokyo "arrives before it left" on the calendar.
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UTC vs GMT
GMT (Greenwich Mean Time) is based on Earth's rotation; UTC is based on atomic clocks. They differ by at most 0.9 seconds. For everyday purposes they are identical. UTC is the preferred technical standard used in computing, aviation, and finance.
Complete Time Zone Reference Table
All major world time zones with UTC offsets, abbreviations, countries, and DST status
Reference
Major World Timezones — UTC Offset Guide
| UTC Offset | Abbreviation | Region / Cities | DST? | Countries |
|---|---|---|---|---|
UTC−12:00 | IDLW | International Date Line West | No | Baker Island, Howland Island |
UTC−11:00 | NUT / SST | Samoa, Niue | No | American Samoa, Niue |
UTC−10:00 | HST | Hawaii, Tahiti | No | USA (Hawaii), French Polynesia |
UTC−09:00 | AKST/AKDT | Alaska | Yes (Mar–Nov) | USA (Alaska) |
UTC−08:00 | PST/PDT | Los Angeles, Vancouver, Seattle | Yes (Mar–Nov) | USA, Canada (Pacific) |
UTC−07:00 | MST/MDT | Denver, Phoenix, Calgary | Yes (except AZ) | USA (Mountain), Canada |
UTC−06:00 | CST/CDT | Chicago, Mexico City, Winnipeg | Yes (Mar–Nov) | USA (Central), Canada, Mexico |
UTC−05:00 | EST/EDT | New York, Miami, Toronto | Yes (Mar–Nov) | USA (Eastern), Canada, Caribbean |
UTC−04:00 | AST / EDT | Halifax, Caracas, Puerto Rico | Varies | Canada (Atlantic), Venezuela |
UTC−03:00 | BRT / ART | São Paulo, Buenos Aires | No | Brazil, Argentina |
UTC−02:00 | GST | South Georgia | No | South Georgia & Sandwich Islands |
UTC−01:00 | AZOT / CVT | Azores, Cape Verde | DST in Azores | Portugal (Azores), Cape Verde |
UTC+00:00 | GMT / UTC / WET | London (winter), Lisbon, Accra | UK/IE: Yes (Mar–Oct) | UK, Ireland, Portugal, Ghana |
UTC+01:00 | CET / BST / WAT | Paris, Berlin, Lagos, London (summer) | EU: Yes (Mar–Oct) | Most of Western/Central Europe, Nigeria |
UTC+02:00 | EET / CAT / CEST | Cairo, Johannesburg, Athens (summer) | Greece/E. Europe: Yes | Egypt, South Africa, Eastern Europe |
UTC+03:00 | MSK / AST / EAT | Moscow, Istanbul, Nairobi, Riyadh | No | Russia (Moscow), Turkey, Kenya, Saudi Arabia |
UTC+03:30 | IRST | Tehran | Yes (IRDT +4:30 in summer) | Iran |
UTC+04:00 | GST / AZT | Dubai, Abu Dhabi, Baku | No | UAE, Oman, Azerbaijan |
UTC+04:30 | AFT | Kabul | No | Afghanistan |
UTC+05:00 | PKT / UZT | Karachi, Islamabad, Tashkent | No | Pakistan, Uzbekistan |
UTC+05:30 | IST | Mumbai, Delhi, Kolkata, Chennai | No | India, Sri Lanka |
UTC+05:45 | NPT | Kathmandu | No | Nepal |
UTC+06:00 | BST / ALMT | Dhaka, Almaty | No | Bangladesh, Kazakhstan |
UTC+07:00 | ICT / WIB | Bangkok, Hanoi, Jakarta | No | Thailand, Vietnam, Indonesia (West) |
UTC+08:00 | CST / SGT / HKT | Beijing, Singapore, Hong Kong, Perth | No | China, Singapore, HK, Australia (WA) |
UTC+09:00 | JST / KST | Tokyo, Seoul, Osaka | No | Japan, South Korea |
UTC+09:30 | ACST / ACDT | Adelaide, Darwin | SA: Yes (Oct–Apr) | Australia (SA, NT) |
UTC+10:00 | AEST / ChST | Sydney, Brisbane, Guam | NSW/VIC: Yes (Oct–Apr) | Australia (East), Guam |
UTC+11:00 | NCT / PONT | New Caledonia, Pohnpei | No | New Caledonia, Micronesia |
UTC+12:00 | NZST / FJT | Auckland, Suva, Fiji | NZ: Yes (Sep–Apr) | New Zealand, Fiji |
UTC+13:00 | NZDT / TOT | Auckland (summer), Tonga | Tonga: No | Tonga, Samoa (summer) |
UTC+14:00 | LINT | Kiritimati (Line Islands) | No | Kiribati (Line Islands) |
Daylight Saving Time (DST) — Complete Guide
Which countries observe DST, when clocks change, and how it affects time zone conversions
DST Reference
Daylight Saving Time: When, Where & Why
Daylight Saving Time (DST) is the practice of advancing clocks by one hour during summer months so that darkness falls later in the evening. It was first proposed by Benjamin Franklin in 1784 as a joke, then seriously proposed by New Zealand entomologist George Hudson in 1895, and widely adopted during World War I to conserve energy.
Today, DST is observed by approximately 70 countries, but the dates differ between the Northern and Southern hemispheres. This creates significant time zone conversion complexity — the offset between New York and London changes by 1 hour in March and again in October each year because they switch on different dates.
| Region | DST Observed? | Clocks Forward | Clocks Back | Offset Change |
|---|---|---|---|---|
| USA (most states) | Yes | 2nd Sunday March | 1st Sunday November | +1 hour (EDT, CDT, MDT, PDT) |
| Canada (most provinces) | Yes | 2nd Sunday March | 1st Sunday November | +1 hour |
| European Union | Yes | Last Sunday March | Last Sunday October | +1 hour (CEST, BST, EEST) |
| United Kingdom | Yes | Last Sunday March | Last Sunday October | UTC+0 → UTC+1 (BST) |
| Australia (SE states) | Yes (reversed) | 1st Sunday October | 1st Sunday April | +1 hour (AEDT, ACDT) |
| New Zealand | Yes (reversed) | Last Sunday September | 1st Sunday April | UTC+12 → UTC+13 (NZDT) |
| Mexico (most) | Yes | 1st Sunday April | Last Sunday October | +1 hour |
| India | No — IST year-round | — | — | Always UTC+5:30 |
| China | No — CST year-round | — | — | Always UTC+8:00 |
| Japan | No — JST year-round | — | — | Always UTC+9:00 |
| Russia | No (abolished 2014) | — | — | Moscow: Always UTC+3 |
| UAE / Saudi Arabia | No | — | — | Always UTC+4 / UTC+3 |
| Most of Africa | No | — | — | Year-round fixed offsets |
| Most of SE Asia | No | — | — | Fixed: SGT, ICT, WIB, etc. |
⚠️ DST Conversion Trap: The time difference between the USA (Eastern) and the UK changes throughout the year. In winter: New York (EST) is UTC-5 and London (GMT) is UTC+0 — a 5-hour gap. But in spring, the US switches DST 2–3 weeks before Europe, creating a temporary 4-hour gap. After Europe switches, it returns to 5 hours. Always use an auto-DST converter for accurate results.
Best Times for International Calls & Meetings
Overlap windows for the world's most common international business and personal call combinations
Meeting Planning
Workable Overlap Windows by City Pair
| City Pair | Time Difference | Best Window (Local Time) | Notes |
|---|---|---|---|
| New York ↔ London | 5 hrs (4 in spring) | 9AM–1PM NYC = 2–6PM London | Excellent overlap — both in business hours |
| New York ↔ Paris/Berlin | 6 hrs (5/7 in transitions) | 9AM–12PM NYC = 3–6PM Europe | Good morning NYC = late afternoon Europe |
| New York ↔ Dubai | 8–9 hrs | 8–9AM NYC = 5–6PM Dubai | Very narrow — early morning NYC required |
| New York ↔ India (IST) | 10.5 hrs | 8–9AM NYC = 6:30–7:30PM IST | Difficult — works for 1–2 hours only |
| New York ↔ Singapore/HK | 12–13 hrs | 8AM NYC = 8–9PM SGT (evening) | Very challenging — one side always sacrifices |
| New York ↔ Tokyo/Seoul | 13–14 hrs | 7–8AM NYC = 8–9PM Tokyo | Early morning NYC, evening Tokyo |
| London ↔ Dubai | 3–4 hrs | 9AM–2PM London = 12–5PM Dubai | Excellent overlap — recommended 9AM–12PM GMT |
| London ↔ India (IST) | 5.5 hrs | 9AM–12PM London = 2:30–5:30PM IST | Very workable — both in business hours |
| London ↔ Singapore | 7–8 hrs | 9AM–11AM London = 4–6PM SGT | Reasonable — late afternoon Singapore |
| London ↔ Sydney | 9–11 hrs | 8AM London = 5–7PM Sydney | Works at early morning London / end of day Sydney |
| Dubai ↔ Singapore | 4 hrs | 9AM–2PM Dubai = 1–6PM SGT | Excellent overlap — both fully in business hours |
| India ↔ Singapore | 2.5 hrs | 9AM–4PM IST = 11:30AM–6:30PM SGT | Excellent — very comfortable overlap all day |
| Singapore ↔ Sydney | 2–3 hrs | 9AM–4PM SGT = 11AM–6PM AEST | Great overlap — both Asia-Pacific, similar hours |
| LA ↔ Tokyo | 17 hrs | 7AM LA = midnight Tokyo (next day) | Almost impossible — one side must work at night |
Time Zone FAQs
Answers to the most commonly asked questions about time zones, UTC, DST, and time conversion
How do I convert time between time zones?
To convert between time zones:
1. Find the UTC offset of your source time zone (e.g. New York = UTC-5 in winter / UTC-4 in summer).
2. Convert to UTC: add your UTC offset to get the UTC time. E.g. 9:00 AM EST + 5 hours = 2:00 PM UTC.
3. Convert from UTC to the target zone: add the target's UTC offset. E.g. UTC 2:00 PM + 5:30 (IST) = 7:30 PM IST.
Our converter handles this automatically, including Daylight Saving Time adjustments.
1. Find the UTC offset of your source time zone (e.g. New York = UTC-5 in winter / UTC-4 in summer).
2. Convert to UTC: add your UTC offset to get the UTC time. E.g. 9:00 AM EST + 5 hours = 2:00 PM UTC.
3. Convert from UTC to the target zone: add the target's UTC offset. E.g. UTC 2:00 PM + 5:30 (IST) = 7:30 PM IST.
Our converter handles this automatically, including Daylight Saving Time adjustments.
What is the difference between UTC and GMT?
UTC (Coordinated Universal Time) and GMT (Greenwich Mean Time) are for all practical purposes the same time — both represent UTC+0. The difference is technical:
• GMT is an astronomical time standard based on Earth's rotation relative to the sun, measured at the Royal Observatory in Greenwich, London.
• UTC is an atomic time standard maintained by 400+ atomic clocks worldwide, coordinated by the BIPM (International Bureau of Weights and Measures).
UTC is the preferred modern standard for computing, aviation, banking, and scientific use. GMT is still used in time zone naming (e.g. "GMT+5:30"). They differ by at most 0.9 seconds and are functionally identical in everyday use.
• GMT is an astronomical time standard based on Earth's rotation relative to the sun, measured at the Royal Observatory in Greenwich, London.
• UTC is an atomic time standard maintained by 400+ atomic clocks worldwide, coordinated by the BIPM (International Bureau of Weights and Measures).
UTC is the preferred modern standard for computing, aviation, banking, and scientific use. GMT is still used in time zone naming (e.g. "GMT+5:30"). They differ by at most 0.9 seconds and are functionally identical in everyday use.
What is Daylight Saving Time and which countries use it?
Daylight Saving Time (DST) is the practice of advancing clocks 1 hour forward in spring ("spring forward") and 1 hour back in autumn ("fall back") so that daylight extends later into the evening during summer months.
Countries that observe DST: USA, Canada, EU nations, UK, Australia (reversed seasons), New Zealand, Mexico, most of South America, and several others (~70 countries total).
Countries that do NOT observe DST: India, China, Japan, most of Africa, UAE, Saudi Arabia, Indonesia, most of Southeast Asia, and Russia (abolished DST in 2014).
DST makes time zone conversion more complex — the difference between two zones can shift by 1 hour at different points in the year.
Countries that observe DST: USA, Canada, EU nations, UK, Australia (reversed seasons), New Zealand, Mexico, most of South America, and several others (~70 countries total).
Countries that do NOT observe DST: India, China, Japan, most of Africa, UAE, Saudi Arabia, Indonesia, most of Southeast Asia, and Russia (abolished DST in 2014).
DST makes time zone conversion more complex — the difference between two zones can shift by 1 hour at different points in the year.
What time zone is UTC+5:30 (IST)?
UTC+5:30 is India Standard Time (IST), used throughout India and Sri Lanka. India does not observe DST, so IST remains UTC+5:30 year-round — one of the few half-hour offset time zones in the world.
IST is 5 hours and 30 minutes ahead of UTC. To convert from IST to major world times:
• IST to GMT: subtract 5 hours 30 minutes
• IST to EST (New York, winter): subtract 10 hours 30 minutes
• IST to PST (LA, winter): subtract 13 hours 30 minutes
• IST to SGT (Singapore): subtract 2 hours 30 minutes
• IST to JST (Tokyo): subtract 3 hours 30 minutes
IST is 5 hours and 30 minutes ahead of UTC. To convert from IST to major world times:
• IST to GMT: subtract 5 hours 30 minutes
• IST to EST (New York, winter): subtract 10 hours 30 minutes
• IST to PST (LA, winter): subtract 13 hours 30 minutes
• IST to SGT (Singapore): subtract 2 hours 30 minutes
• IST to JST (Tokyo): subtract 3 hours 30 minutes
How many time zones does the USA have?
The United States uses 9 time zones across its territories:
1. EST/EDT (UTC-5/-4) — Eastern: New York, Miami, Boston, Washington DC
2. CST/CDT (UTC-6/-5) — Central: Chicago, Dallas, Houston, New Orleans
3. MST/MDT (UTC-7/-6) — Mountain: Denver, Phoenix (no DST), Salt Lake City
4. PST/PDT (UTC-8/-7) — Pacific: Los Angeles, San Francisco, Seattle
5. AKST/AKDT (UTC-9/-8) — Alaska
6. HST (UTC-10) — Hawaii (no DST)
7. SST (UTC-11) — American Samoa
8. ChST (UTC+10) — Guam, Northern Mariana Islands
9. UTC+12 — Wake Island
The contiguous 48 states span 4 time zones (Eastern to Pacific).
1. EST/EDT (UTC-5/-4) — Eastern: New York, Miami, Boston, Washington DC
2. CST/CDT (UTC-6/-5) — Central: Chicago, Dallas, Houston, New Orleans
3. MST/MDT (UTC-7/-6) — Mountain: Denver, Phoenix (no DST), Salt Lake City
4. PST/PDT (UTC-8/-7) — Pacific: Los Angeles, San Francisco, Seattle
5. AKST/AKDT (UTC-9/-8) — Alaska
6. HST (UTC-10) — Hawaii (no DST)
7. SST (UTC-11) — American Samoa
8. ChST (UTC+10) — Guam, Northern Mariana Islands
9. UTC+12 — Wake Island
The contiguous 48 states span 4 time zones (Eastern to Pacific).
Why does China use only one time zone?
China officially uses a single time zone — China Standard Time (CST, UTC+8) — despite spanning approximately 60° of longitude (roughly 5 natural time zones, from UTC+5 to UTC+9).
This was a political decision made by the Communist government in 1949 to promote national unity under Chairman Mao. Prior to 1949, China used 5 time zones.
The result is that in western China (Xinjiang province), the sun rises and sets very late relative to the clock — sunrise can be as late as 10 AM in winter. Many Uyghur people in Xinjiang informally use "Xinjiang time" (UTC+6), which better matches natural solar time there.
For comparison, Russia — which also spans enormous longitude — uses 11 separate time zones, the most of any single country.
This was a political decision made by the Communist government in 1949 to promote national unity under Chairman Mao. Prior to 1949, China used 5 time zones.
The result is that in western China (Xinjiang province), the sun rises and sets very late relative to the clock — sunrise can be as late as 10 AM in winter. Many Uyghur people in Xinjiang informally use "Xinjiang time" (UTC+6), which better matches natural solar time there.
For comparison, Russia — which also spans enormous longitude — uses 11 separate time zones, the most of any single country.
What is the best time for a US–India video call?
The US–India time difference is large (10.5–13.5 hours depending on US city and DST), making overlap very difficult:
New York (EST, UTC-5) ↔ India (IST, UTC+5:30):
• Difference: 10 hours 30 minutes
• Best window: 7:30–9:00 AM EST = 6:00–7:30 PM IST
• Workable but requires early morning for US side
Los Angeles (PST, UTC-8) ↔ India (IST, UTC+5:30):
• Difference: 13 hours 30 minutes
• Best window: 6:30–8:00 AM PST = 8:00–9:30 PM IST
• Very challenging — evening for India, very early for LA
The most common approach is for US teams to take early morning calls (7–9 AM EST) while India joins at the end of their work day (5:30–7:30 PM IST). In summer (EDT), the gap narrows to 9.5 hours for New York.
New York (EST, UTC-5) ↔ India (IST, UTC+5:30):
• Difference: 10 hours 30 minutes
• Best window: 7:30–9:00 AM EST = 6:00–7:30 PM IST
• Workable but requires early morning for US side
Los Angeles (PST, UTC-8) ↔ India (IST, UTC+5:30):
• Difference: 13 hours 30 minutes
• Best window: 6:30–8:00 AM PST = 8:00–9:30 PM IST
• Very challenging — evening for India, very early for LA
The most common approach is for US teams to take early morning calls (7–9 AM EST) while India joins at the end of their work day (5:30–7:30 PM IST). In summer (EDT), the gap narrows to 9.5 hours for New York.
What is the International Date Line?
The International Date Line (IDL) is an imaginary line at approximately 180° longitude in the Pacific Ocean where the calendar date changes. It was established in 1884 alongside the global time zone system.
Crossing the IDL:
• Westbound (travelling from Americas to Asia/Pacific): you gain a day — your calendar date advances by 1.
• Eastbound (travelling from Asia/Pacific to Americas): you lose a day — your calendar date goes back by 1.
This is why a flight from Los Angeles to Tokyo can appear to "arrive the next day," while a flight from Tokyo to LA can "arrive on the same day it departed" — or even a day earlier on the calendar. The IDL is not a straight line — it zigzags around island nations so that politically connected islands share the same date.
Crossing the IDL:
• Westbound (travelling from Americas to Asia/Pacific): you gain a day — your calendar date advances by 1.
• Eastbound (travelling from Asia/Pacific to Americas): you lose a day — your calendar date goes back by 1.
This is why a flight from Los Angeles to Tokyo can appear to "arrive the next day," while a flight from Tokyo to LA can "arrive on the same day it departed" — or even a day earlier on the calendar. The IDL is not a straight line — it zigzags around island nations so that politically connected islands share the same date.
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