MDT to AST Converter
Convert time between Mountain Daylight Time (MDT) and Atlantic Standard Time (AST)
Mountain Daylight Time (MDT)
Atlantic Standard Time (AST)
Time Difference
Atlantic Standard Time (AST) is 0 hours ahead of Mountain Daylight Time (MDT)
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Select Time
Quick Reference
| MDT | AST |
|---|---|
| 19:00 | 22:00 |
| 21:00 | 00:00 |
| 23:00 | 02:00 |
| 01:00 | 04:00 |
| 03:00 | 06:00 |
| 05:00 | 08:00 |
| 07:00 | 10:00 |
| 09:00 | 12:00 |
| 11:00 | 14:00 |
| 13:00 | 16:00 |
| 15:00 | 18:00 |
| 17:00 | 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 MDT to AST Time Conversion
Converting time between Mountain Daylight Time (MDT) and Atlantic Standard Time (AST) is essential for coordinating between the Mountain region of the US and Atlantic Canada. MDT is UTC-6 (March to November during daylight saving time), while AST is UTC-4 (year-round in Atlantic provinces). AST is exactly 2 hours ahead of MDT.
This conversion is crucial for businesses with operations spanning the US Mountain region and Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland and Labrador). The Atlantic region does not observe daylight saving time, making this a stable 2-hour offset throughout the year. Companies coordinating across this international border require accurate time conversions for supply chain management, remote work coordination, and business continuity.
Common Use Cases for MDT to AST Conversion
Business & Work
- Scheduling business calls between US Mountain offices and Atlantic Canadian offices
- Coordinating supply chain operations across US-Canada border
- Managing distributed teams spanning Mountain US and Atlantic Canada
- International business meetings with Halifax or Saint John offices
Personal & Travel
- Planning travel between Mountain region and Atlantic Canada
- Coordinating with Canadian family and friends in Atlantic provinces
- Scheduling virtual meetings with Canadian business partners
- Understanding time differences for international remote work
Time Zone Information
Mountain Daylight Time (MDT)
- UTC Offset: UTC-6 (UTC-7 during MST)
- IANA Timezone: America/Denver
- Daylight Saving: Second Sunday in March to First Sunday in November
- Major Cities: Denver, Salt Lake City, Albuquerque, Boise, Fort Collins
- Coverage: Mountain United States and parts of Canada
Atlantic Standard Time (AST)
- UTC Offset: UTC-4 (Year-round, no daylight saving)
- IANA Timezone: America/Halifax
- Daylight Saving: No daylight saving time - consistent year-round
- Major Cities: Halifax, Saint John, Fredericton, Moncton, St. John's
- Coverage: Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador)
Quick Reference: MDT to AST
Remember: AST is always 2 hours ahead of MDT. Unlike most North American regions, Atlantic Canada does not observe daylight saving time, so the 2-hour offset remains consistent year-round.
Frequently Asked Questions
What is the time difference between MDT and AST?
Mountain Daylight Time (MDT) is UTC-6, while Atlantic Standard Time (AST) is UTC-4. This means AST is 2 hours ahead of MDT. When it's 12:00 PM noon in Denver (MDT), it's 2:00 PM in Halifax (AST).
Why does Atlantic Canada not observe daylight saving time?
Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island) has chosen not to observe daylight saving time, keeping Atlantic Standard Time (AST) at UTC-4 year-round. This is unique among major North American regions and means the time offset between Mountain and Atlantic regions changes seasonally - 2 hours during MDT season and 3 hours during MST season.
What is the time difference when the Mountain region is in standard time?
From November to March, the Mountain region observes Mountain Standard Time (MST) at UTC-7. Atlantic Canada remains at UTC-4 (AST), making the difference 3 hours instead of 2 hours. This is a key factor for year-round business coordination - you must adjust your calculation based on the season.
Which major cities are in the Atlantic timezone?
Atlantic Standard Time covers Atlantic Canadian cities including Halifax (Nova Scotia), Saint John (New Brunswick), Fredericton (New Brunswick), Moncton (New Brunswick), and St. John's (Newfoundland and Labrador). These regions serve as major business and trade hubs for Atlantic Canada.
What are the best times to schedule calls between Mountain and Atlantic regions?
With a 2-hour difference during daylight saving (MDT), morning Mountain meetings (9-10 AM MDT) align with late morning Atlantic (11 AM-12 PM AST). Afternoon Mountain meetings (3-4 PM MDT) correspond to evening Atlantic (5-6 PM AST). Remember the difference increases to 3 hours during winter months (November-March).
Why is this conversion important for US-Canada business?
Atlantic Canada is a major trade hub with significant oil and gas, fishing, and manufacturing industries. Companies with operations spanning the US Mountain region (Denver, Salt Lake City) and Atlantic Canada must navigate the unique time difference that changes seasonally. The lack of daylight saving time in Atlantic Canada makes year-round coordination slightly more complex than between US regions.
Pro Tips
- • Remember: Atlantic Canada does NOT observe daylight saving time - AST is UTC-4 year-round, making it 2 hours ahead of MDT and 3 hours ahead of MST.
- • During MDT season (March-November): 9 AM MDT = 11 AM AST. During MST season (November-March): 9 AM MST = 12 PM AST.
- • Schedule international meetings carefully - the time difference varies by season, so document times in both timezones to avoid confusion.
- • Halifax business hours (9 AM-5 PM AST) correspond to 7 AM-3 PM MDT - schedule important calls before 3 PM MDT to catch Atlantic business hours.
- • For year-round recurring meetings, use the winter time (MST-AST = 3 hours) as the safer baseline, then adjust during summer.
- • Supply chain coordination across the US-Canada border requires attention to both timezone differences and daylight saving transitions in the Mountain region.
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