AST to MDT Converter
Convert time between Atlantic Standard Time (AST) and Mountain Daylight Time (MDT)
Atlantic Standard Time (AST)
Mountain Daylight Time (MDT)
Time Difference
Mountain Daylight Time (MDT) is 0 hours ahead of Atlantic Standard Time (AST)
Select Date
Select Time
Quick Reference
| AST | MDT |
|---|---|
| 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 MDT Time Conversion
Converting time between Atlantic Standard Time (AST) and Mountain Daylight Time (MDT) is unique because these two zones only overlap during a specific seasonal window. AST is UTC-4 and is only active from the first Sunday in November through the second Sunday in March (winter months). MDT is UTC-6 and is active from the second Sunday in March through the first Sunday in November (summer months). When both are active simultaneously (late March through early April only), AST is 2 hours ahead of MDT.
This conversion is most relevant during the spring transition period in March and April when Atlantic Canada remains in standard time while the Mountain region has already switched to daylight time. After Atlantic Canada transitions to Atlantic Daylight Time (ADT, UTC-3), the difference becomes 3 hours. Understanding the seasonal nature of this conversion is crucial for accurate scheduling, especially for businesses coordinating between Atlantic Canada and the US Mountain region during spring and early summer months. The brief 2-hour window makes this one of the more specialized timezone conversions.
Common Use Cases for AST to MDT Conversion
Business & Work
- Scheduling meetings between Atlantic Canada and Mountain region offices during spring transition
- Coordinating software development teams across regions during March-April period
- Managing business operations with Mountain region partners during spring months
- Planning conference calls and project deadlines during seasonal transitions
Personal & Travel
- Coordinating with family and friends in the Mountain region during spring months
- Planning spring 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 (Winter only, November-March)
- IANA Timezone: America/Halifax
- Daylight Saving: Active only November to March. Transitions to ADT (UTC-3) on second Sunday in March
- Major Cities: Halifax, Saint John, Charlottetown, Fredericton
- Coverage: Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island)
Mountain Daylight Time (MDT)
- UTC Offset: UTC-6 (Summer only, March-November)
- IANA Timezone: America/Denver
- Daylight Saving: Active March to November. Transitions from MST (UTC-7) on second Sunday in March
- Major Cities: Denver, Salt Lake City, Albuquerque, Boise
- Coverage: Mountain United States and Canada (summer months)
Quick Reference: AST to MDT
Remember: AST is 2 hours ahead of MDT. This conversion only applies from late March to early April when Atlantic is still on standard time and Mountain has switched to daylight time. After Atlantic switches to ADT, the difference becomes 3 hours.
Frequently Asked Questions
What is the time difference between AST and MDT?
Atlantic Standard Time (AST) is UTC-4, while Mountain Daylight Time (MDT) is UTC-6. This means AST is 2 hours ahead of MDT. When it's 12:00 PM (noon) in Halifax (AST), it's 10:00 AM in Denver (MDT). Note: This 2-hour difference occurs during spring and summer months when Atlantic Daylight Time (ADT, UTC-3) is active simultaneously with MDT. From November to March, Atlantic is on AST (UTC-4) while Mountain is on MST (UTC-7), creating a 3-hour difference.
How does the AST to MDT offset differ from other Atlantic-US conversions?
The 2-hour offset between AST and MDT represents a unique seasonal window (late March to first Sunday in November). AST is only used during winter months, so this conversion applies when Atlantic Daylight Time (ADT, UTC-3) is actually active. The relationship is more complex: during ADT-MDT overlap, the difference is 3 hours. This makes Atlantic-Mountain coordination highly dependent on which daylight saving season you're in. Both regions transition on the same dates, but AST refers specifically to winter time.
When is AST active and how does it relate to MDT?
Atlantic Standard Time (AST) is active from the first Sunday in November through the second Sunday in March. Mountain Daylight Time (MDT) is active from the second Sunday in March through the first Sunday in November. These periods overlap from mid-March to early November, creating a 2-hour difference. Before mid-March, Atlantic is still in AST while Mountain is transitioning to MDT. After early November, Atlantic transitions to AST while Mountain remains in MDT briefly. The transition dates matter significantly for scheduling.
What are the actual time differences during different seasons?
The time differences vary by season: March-November (ADT-MDT overlap): 3 hours, November-March (AST-MST): 3 hours, Second Sunday March-First Sunday November (ADT-MDT): 3 hours. Wait, this is complex! When you specifically reference AST to MDT, you're describing the brief period when Atlantic is still in standard time (AST, UTC-4) while Mountain has already switched to daylight time (MDT, UTC-6). This occurs only from second Sunday in March to early April, creating a 2-hour difference. Always verify current dates when scheduling.
What are the best times to schedule calls between Atlantic Canada and Mountain region during spring/summer?
When AST-MDT applies (March-April period), business hour overlap exists but is limited. Atlantic morning (9 AM-12 PM AST) overlaps with Mountain early morning (7 AM-10 AM MDT). Mountain afternoon (2 PM-5 PM MDT) overlaps with Atlantic late afternoon (4 PM-7 PM AST). The 9-10 AM AST window (7-8 AM MDT) works for early birds, while the 3-4 PM MDT window (5-6 PM AST) accommodates evening schedules. After early April when Atlantic switches to ADT, the difference becomes 3 hours, improving overlap opportunities.
How do daylight saving transitions affect AST-MDT scheduling?
Both regions transition to daylight saving on the second Sunday in March, but the practical effect differs. Atlantic switches from AST (UTC-4) to ADT (UTC-3) on the same day Mountain switches from MST (UTC-7) to MDT (UTC-6). Between mid-March and early April, when AST technically remains as standard time, the offset is 2 hours. Once Atlantic switches to ADT, the offset becomes 3 hours. Document transition dates carefully and update all meeting schedules when daylight saving changes occur to avoid confusion.
Pro Tips
- • AST to MDT is a unique 2-hour difference that only applies during a brief spring period (March-April). Most of the year involves ADT-MDT (3 hours) or AST-MST (3 hours).
- • Mark the transition dates on your calendar: second Sunday in March (both regions change), first Sunday in November (both regions change back). These dates determine which timezone conversion applies.
- • During the short AST-MDT window (mid-March to early April), schedule Atlantic morning meetings (9-10 AM AST) to catch Mountain early risers (7-8 AM MDT).
- • Once Atlantic switches to ADT in April, the offset changes to 3 hours. Update all recurring meeting schedules when this transition occurs to prevent scheduling confusion.
- • If you need consistent timezone conversions, consider scheduling important meetings in May-October when ADT-MDT provides a stable 3-hour difference or wait until winter for AST-MST stability.
- • Use this calculator to verify times during the spring transition period when daylight saving changes could create scheduling errors or double-booked meetings.
Update Logs
View the latest updates and features