GMT to AST Converter
Convert time between Greenwich Mean Time (GMT) and Atlantic Standard Time (AST)
Greenwich Mean Time (GMT)
Atlantic Standard Time (AST)
Time Difference
Atlantic Standard Time (AST) is 0 hours ahead of Greenwich Mean Time (GMT)
Select Date
Select Time
Quick Reference
| GMT | AST |
|---|---|
| 02:00 | 22:00 |
| 04:00 | 00:00 |
| 06:00 | 02:00 |
| 08:00 | 04:00 |
| 10:00 | 06:00 |
| 12:00 | 08:00 |
| 14:00 | 10:00 |
| 16:00 | 12:00 |
| 18:00 | 14:00 |
| 20:00 | 16:00 |
| 22:00 | 18:00 |
| 00:00 | 20:00 |
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 GMT to AST Time Conversion
Converting time from Greenwich Mean Time (GMT) to Atlantic Standard Time (AST) is essential for UK to Atlantic Canada coordination. GMT is UTC+0, while AST is UTC-4, making AST 4 hours behind GMT.
This conversion is crucial for international business operations between the United Kingdom and Atlantic Canada, including major cities like Halifax, St. John's, and Saint John. Whether you're scheduling meetings, coordinating project deadlines, or planning travel, our accurate IANA-based converter ensures you never miss the time difference.
Common Use Cases for GMT to AST Conversion
Business & Work
- Scheduling UK to Atlantic Canada business meetings
- Coordinating London and Halifax operations
- Managing international maritime and energy sector operations
- Planning conference calls with distributed teams
Personal & Travel
- Planning travel from UK to Atlantic Canada (Nova Scotia, New Brunswick, Newfoundland)
- Coordinating with Atlantic Canada family and friends from UK
- Scheduling virtual events and online meetings for UK-Atlantic Canada audiences
- Arranging online classes or training sessions
Time Zone Information
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
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, St. John's, Charlottetown
- Coverage: Atlantic Canada and parts of Caribbean
Quick Reference: GMT to AST
Remember: AST is always 4 hours behind GMT. This conversion applies when Atlantic Canada observes AST (November to March). During ADT (March to November), the difference becomes 3 hours.
Frequently Asked Questions
What is the time difference between GMT and AST?
Greenwich Mean Time (GMT) is UTC+0, while Atlantic Standard Time (AST) is UTC-4. This means GMT is 4 hours ahead of AST. When it's 12:00 PM (noon) in London (GMT), it's 8:00 AM in Halifax (AST).
Does Atlantic Canada use AST year-round?
No, Atlantic Canada switches between AST (UTC-4) in winter and ADT (Atlantic Daylight Time, UTC-3) in summer. ADT is active from the second Sunday in March to the first Sunday in November. This means when Canada observes ADT, the time difference to GMT becomes only 3 hours instead of 4.
Does the UK use GMT year-round?
No, the UK switches between GMT (UTC+0) in winter and BST (British Summer Time, UTC+1) in summer. BST is active from the last Sunday in March to the last Sunday in October. This means when the UK observes BST, the time difference to AST becomes only 5 hours instead of 4.
When do GMT and AST transitions occur?
GMT and AST transition at different times. The UK transitions on the last Sunday in March and October, while Atlantic Canada transitions on the second Sunday in March and first Sunday in November. These different transition dates mean the offset between GMT and AST can vary slightly throughout the year.
What are the best times to schedule calls between UK and Atlantic Canada?
Morning in the UK (9-11 AM GMT) overlaps with early morning in Atlantic Canada (5-7 AM AST). Afternoon in the UK (2-4 PM GMT) overlaps with late morning in Atlantic Canada (10 AM-12 PM AST). For optimal business hours overlap, schedule meetings between 2-4 PM UK time (10 AM-12 PM AST).
Why is GMT to AST conversion important?
GMT to AST conversion is essential for coordinating between the United Kingdom and Atlantic Canada, which includes major cities like Halifax, St. John's, and Saint John. This conversion is vital for business operations, telecommunications, and personal communications between these regions.
Pro Tips
- • The 4-hour difference means 8 AM in London equals 4 AM in Halifax - plan calls strategically to avoid extreme hours.
- • UK and Atlantic Canada transition on different dates, so the offset can be 3, 4, or 5 hours depending on the time of year.
- • Schedule important UK-Atlantic Canada meetings in early afternoon UK time (2-4 PM GMT, 10 AM-12 PM AST) for the best business hours overlap.
- • Remember that Atlantic Canada observes ADT (3-hour difference) from March to November, not AST (4-hour difference).
- • Use the 3 PM GMT window (11 AM AST) for late morning meetings on the Atlantic Canada side while catching UK business hours.
- • For 24/7 operations with UK-Atlantic Canada teams, split-shift scheduling is essential - UK afternoon/evening covers Atlantic Canada morning.
Update Logs
View the latest updates and features