AST to MST Converter
Convert time between Atlantic Standard Time (AST) and Mountain Standard Time (MST)
Atlantic Standard Time (AST)
Mountain Standard Time (MST)
Time Difference
Mountain Standard Time (MST) is 0 hours ahead of Atlantic Standard Time (AST)
Select Date
Select Time
Quick Reference
| AST | MST |
|---|---|
| 22:00 | 19:00 |
| 00:00 | 21:00 |
| 02:00 | 23:00 |
| 04:00 | 01:00 |
| 06:00 | 03:00 |
| 08:00 | 05:00 |
| 10:00 | 07:00 |
| 12:00 | 09:00 |
| 14:00 | 11:00 |
| 16:00 | 13:00 |
| 18:00 | 15:00 |
| 20:00 | 17:00 |
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 MST Time Conversion
Converting time between Atlantic Standard Time (AST) and Mountain Standard Time (MST) is essential for coordinating across North America from Atlantic Canada to the US Mountain region. AST is UTC-4 (the standard time in Atlantic Canada, used November to March), while MST is UTC-7 (standard time on the US Mountain, typically November to March). AST is 3 hours ahead of MST.
This conversion is crucial for business coordination between Atlantic Canada and the US Mountain region. Companies in Denver, Salt Lake City, and other Mountain region cities frequently coordinate with Atlantic Canadian offices in Halifax and other maritime centers. When daylight saving time transitions occur (second Sunday in March and first Sunday in November), both regions shift simultaneously, with the time difference becoming 2 hours (ADT to MDT). Understanding these transitions is essential for accurate scheduling and maintaining effective cross-regional business operations.
Common Use Cases for AST to MST Conversion
Business & Work
- Scheduling meetings between Atlantic Canada and Mountain region offices
- Coordinating software development teams across Atlantic and Mountain zones
- Managing business operations with Mountain region partners and clients
- Planning conference calls and project deadlines across regions
Personal & Travel
- Coordinating with family and friends in the Mountain region
- Planning travel from Atlantic Canada to Mountain destinations
- Scheduling virtual meetings with Mountain region relatives
- Arranging online collaboration with Mountain region-based colleagues
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, Fredericton
- Coverage: Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island)
Mountain Standard Time (MST)
- UTC Offset: UTC-7 (UTC-6 during MDT)
- IANA Timezone: America/Denver
- Daylight Saving: Second Sunday in March to First Sunday in November
- Major Cities: Denver, Salt Lake City, Albuquerque, Boise
- Coverage: Mountain United States and Canada (winter months)
Quick Reference: AST to MST
Remember: AST is 3 hours ahead of MST during winter (November-March). From March to November when ADT and MDT are active, the difference becomes 2 hours (ADT to MDT).
Frequently Asked Questions
What is the time difference between AST and MST?
Atlantic Standard Time (AST) is UTC-4, while Mountain Standard Time (MST) is UTC-7. This means AST is 3 hours ahead of MST. When it's 12:00 PM (noon) in Halifax (AST), it's 9:00 AM in Denver (MST). Note: This 3-hour difference applies during winter months when AST is active. From March to November, when Atlantic Daylight Time (ADT, UTC-3) is active, the difference becomes 2 hours.
How does the AST to MST offset differ from other Atlantic-US conversions?
The 3-hour offset between AST and MST is moderate compared to Atlantic-Pacific conversions (which are 4 hours). This makes Atlantic-Mountain coordination more manageable than Atlantic-Pacific. The offset remains consistent except during daylight saving transitions. AST and MST transition to daylight time on the same schedule (second Sunday in March, first Sunday in November), which simplifies calendar management. The 3-hour difference provides reasonable business hour overlap compared to longer transatlantic or transpacific differences.
Does Mountain region observe daylight saving time like Atlantic Canada?
Yes, both regions observe daylight saving time on the same dates (second Sunday in March to first Sunday in November). During these periods, the Mountain region observes Mountain Daylight Time (MDT, UTC-6) and Atlantic Canada observes Atlantic Daylight Time (ADT, UTC-3). This reduces the time difference from 3 hours (AST-MST) to 2 hours (ADT-MDT). From November to March, AST and MST are active with the full 3-hour difference.
When does the time difference change from 3 to 2 hours?
The difference changes on the second Sunday in March when both regions transition to daylight saving time (ADT and MDT). From March to November, the difference is 2 hours (ADT to MDT). From November to March, the difference is 3 hours (AST to MST). Both regions use the same transition dates, making it easier to remember and adjust your calendar. Mark these dates: second Sunday in March (spring forward) and first Sunday in November (fall back).
What are the best times to schedule calls between Atlantic Canada and Mountain region?
Business hour overlap is moderate with a 3-hour difference (winter) or 2-hour difference (summer). Atlantic morning (9 AM-12 PM AST) overlaps with Mountain early morning (6 AM-9 AM MST). Mountain afternoon (2 PM-5 PM MST) overlaps with Atlantic evening (5 PM-8 PM AST). For winter months, 9-10 AM AST equals 6-7 AM MST, offering a comfortable window for Mountain teams starting work. This 9 AM AST to 5 PM MST window provides good coverage for both regions.
Why coordinate between Atlantic Canada and Mountain US regions?
Atlantic Canada and the US Mountain region connect two important economic zones. Atlantic Canada (Halifax, Saint John) serves as a tech and business hub, while the Mountain region (Denver, Salt Lake City) hosts major corporate headquarters, tech companies, and government operations. The 3-hour time difference makes cross-region coordination feasible compared to Pacific routes. Companies in energy, technology, finance, and business services frequently coordinate between these regions, making reliable timezone conversion essential.
Pro Tips
- • Remember the 3-hour offset (winter) or 2-hour offset (summer). The difference changes only on daylight saving transition dates (second Sunday in March and first Sunday in November).
- • Both regions transition to daylight saving on the same dates. Mark your calendar to update meeting schedules immediately when these transitions occur.
- • Schedule Atlantic team morning meetings (9-10 AM AST) to catch Mountain region teams at 6-7 AM MST for early risers or overnight shift coverage.
- • Use the 10 AM-12 PM MST window (1-3 PM AST) for discussions when both regions are actively in the afternoon workday.
- • During winter (AST-MST, 3-hour difference), 9 AM AST equals 6 AM MST - better for Mountain West Coast early schedules than East Coast offices.
- • Document all meeting times in both AST and MST, noting whether daylight saving time is active to prevent confusion during transitions.
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