AST to GMT Converter
Convert time between Atlantic Standard Time (AST) and Greenwich Mean Time (GMT)
Atlantic Standard Time (AST)
Greenwich Mean Time (GMT)
Time Difference
Greenwich Mean Time (GMT) is 0 hours ahead of Atlantic Standard Time (AST)
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Select Time
Quick Reference
| AST | GMT |
|---|---|
| 22:00 | 02:00 |
| 00:00 | 04:00 |
| 02:00 | 06:00 |
| 04:00 | 08:00 |
| 06:00 | 10:00 |
| 08:00 | 12:00 |
| 10:00 | 14:00 |
| 12:00 | 16:00 |
| 14:00 | 18:00 |
| 16:00 | 20:00 |
| 18:00 | 22:00 |
| 20:00 | 00:00 |
Top 10 Most Common Time Zones
| Abbreviation | Full Name | UTC Offset | Typical Use |
|---|---|---|---|
| UTC | Coordinated Universal Time | UTC ±0 | Global reference standard (servers, logs, APIs) |
| EST / EDT | Eastern (US) Time | UTC −5 / −4 | New York, Toronto — North American business hub |
| CST / CDT | Central (US) Time | UTC −6 / −5 | Chicago, Dallas — US central business region |
| PST / PDT | Pacific (US) Time | UTC −8 / −7 | San Francisco, Los Angeles — tech industry standard |
| GMT / BST | Greenwich Mean / British Summer Time | UTC 0 / +1 | UK, used globally as a reference with UTC |
| CET / CEST | Central European (Summer) Time | UTC +1 / +2 | Paris, Berlin, Amsterdam — EU business core |
| IST | India Standard Time | UTC +5:30 | India — major IT & outsourcing region |
| CST | China Standard Time | UTC +8 | Beijing, Shanghai — East Asia business hub |
| JST | Japan Standard Time | UTC +9 | Tokyo — finance & tech hub |
| AEST / AEDT | Australian Eastern (Daylight) Time | UTC +10 / +11 | Sydney, Melbourne — APAC regional business |
Why Time Zone Abbreviations Are Ambiguous
Unlike standardized identifiers (like America/New_York or Europe/London from the IANA tz database), abbreviations such as "CST" or "IST" are not globally unique. They can refer to different time zones depending on context — country, region, or even time of year (due to daylight saving time).
Common Ambiguous Time Zone Abbreviations
| Abbrev. | Common Meaning(s) | UTC Offset | Region(s) |
|---|---|---|---|
| CST | Central Standard Time / China Standard Time / Cuba Standard Time | UTC−6 / UTC+8 / UTC−5 | North America, China, Cuba |
| IST | Indian Standard Time / Irish Standard Time / Israel Standard Time | UTC+5:30 / UTC+1 / UTC+2 | India, Ireland, Israel |
| AST | Atlantic Standard Time / Arabia Standard Time | UTC−4 / UTC+3 | Caribbean, Canada, Middle East |
| PST | Pacific Standard Time / Philippine Standard Time | UTC−8 / UTC+8 | North America, Philippines |
| EST | Eastern Standard Time (North America / Australia) | UTC−5 / UTC+10 | North America, Australia |
✅ Best Practice
To avoid ambiguity, always:
- Use IANA tz identifiers — e.g.,
America/New_Yorkinstead of "EST" - Specify UTC offset explicitly — e.g.,
UTC−5when abbreviations must be used - Include the full timezone name — e.g., "Eastern Standard Time (EST)" with UTC offset
Related Time Zone Conversions
About AST to GMT Time Conversion
Converting time from Atlantic Standard Time (AST) to Greenwich Mean Time (GMT) is essential for Atlantic Canada to UK coordination. AST is UTC-4, while GMT is UTC+0, making GMT 4 hours ahead of AST.
This conversion is crucial for business operations coordinating between Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island) and the United Kingdom, as well as international communications during the winter months.
Common Use Cases for AST to GMT Conversion
Business & Work
- Scheduling meetings between Atlantic Canada and UK offices
- Coordinating business operations across the Atlantic
- Planning international project collaborations
Personal & Travel
- Planning travel between Atlantic Canada and UK
- Coordinating with UK family and friends
- Scheduling virtual events for Atlantic Canada-UK audiences
Time Zone Information
Atlantic Standard Time (AST)
- UTC Offset: UTC-4 (UTC-3 during ADT)
- IANA Timezone: America/Halifax
- Daylight Saving: Second Sunday in March to First Sunday in November
- Major Cities: Halifax, Saint John, Charlottetown, St. John's
- Coverage: Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador)
Greenwich Mean Time (GMT)
- UTC Offset: UTC+0 (UTC+1 during BST)
- IANA Timezone: Europe/London
- Daylight Saving: Last Sunday in March to Last Sunday in October
- Major Cities: London, Edinburgh, Cardiff, Belfast, Dublin
- Coverage: United Kingdom and Ireland
Quick Reference: AST to GMT
Remember: GMT is always 4 hours ahead of AST
Frequently Asked Questions
What is the time difference between AST and GMT?
Atlantic Standard Time (AST) is UTC-4, while GMT (Greenwich Mean Time) is UTC+0, making GMT 4 hours ahead of AST. When it is 12:00 PM (noon) in Atlantic regions like Halifax or Puerto Rico (AST), it is 4:00 PM the same day in London (GMT).
How does AST differ from ADT?
AST (Atlantic Standard Time) is UTC-4 and is observed during standard time (November to March), while ADT (Atlantic Daylight Time) is UTC-3 and is observed during daylight saving time (March to November). This one-hour difference is important when scheduling across seasons in Atlantic regions.
Does GMT observe daylight saving time?
No, GMT (Greenwich Mean Time) does not observe daylight saving time year-round. However, the UK uses BST (British Summer Time) during daylight saving periods (late March to late October). GMT remains UTC+0 and serves as a global standard reference throughout the year.
When does AST change to ADT?
Atlantic Standard Time (AST) transitions to Atlantic Daylight Time (ADT) on the second Sunday in March at 2:00 AM. The reverse transition from ADT to AST occurs on the first Sunday in November at 2:00 AM. During ADT, the time difference with GMT is only 3 hours instead of 4.
How do I convert AST to GMT manually?
To convert AST to GMT, simply add 4 hours to the AST time. For example, if it is 3:00 PM AST, the corresponding GMT time would be 7:00 PM (15:00 + 4 hours = 19:00). If the result exceeds 24 hours, subtract 24 hours and add 1 day.
Why is understanding AST to GMT conversion important?
Understanding AST to GMT conversion is crucial for coordinating with teams in Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island) and the UK/Europe, international travel planning, virtual meetings across the Atlantic, and managing global business operations. The 4-hour difference makes accurate conversion essential.
Pro Tips
- • AST is observed from November to March. From March to November, Atlantic regions use ADT (Atlantic Daylight Time) with a 3-hour difference from GMT.
- • GMT is equivalent to UTC (Coordinated Universal Time) and serves as the global reference time used for aviation and international business.
- • The UK switches to BST (British Summer Time) at the same dates as AST transitions to ADT, so the time difference changes from 4 hours to 3 hours during overlapping periods.
- • When scheduling international meetings between Atlantic Canada and UK, early morning AST (7-8 AM) aligns with 11 AM-12 PM GMT, making it ideal for both regions.
- • Use a converter like this one for daylight saving transitions to avoid miscalculations when AST switches to ADT and GMT switches to BST.
- • Always verify whether your meeting participants are observing daylight saving time, as transition dates can vary between Atlantic Canada and UK by a few weeks.
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