AST to MDT Converter & Meeting Planner
Quick answer: 9:00 AM AST = 7:00 AM MDT (fixed -04:00 standard offset — not DST-adjusted). Use the interactive converter below for DST-aware local-time scheduling.
Planning a call or meeting between Atlantic Standard Time (AST) and Mountain Daylight Time (MDT)? You need to account for the standard time difference. Mountain Daylight Time is normally 2 hours behind Atlantic Standard Time. Whether you are coordinating between teams in Halifax and San Juan and Denver and Salt Lake City, our live tool has you covered. Use our interactive overlap studio below to find the perfect waking hours for both regions, taking into account any seasonal Daylight Saving Time (DST) changes.
24-Hour Conversion Table
Quick reference: 12:00 AM AST = 10:00 PM MDT. The full 24-hour AST to MDT table below uses fixed standard offsets for exact abbreviation searches.
Example: 3:00 PM AST = 1:00 PM MDT.
| AST Time | MDT Time |
|---|---|
| 12:00 AM (00:00) | 10:00 PM (22:00)-1 day |
| 1:00 AM (01:00) | 11:00 PM (23:00)-1 day |
| 2:00 AM (02:00) | 12:00 AM (00:00) |
| 3:00 AM (03:00) | 1:00 AM (01:00) |
| 4:00 AM (04:00) | 2:00 AM (02:00) |
| 5:00 AM (05:00) | 3:00 AM (03:00) |
| 6:00 AM (06:00) | 4:00 AM (04:00) |
| 7:00 AM (07:00) | 5:00 AM (05:00) |
| 8:00 AM (08:00) | 6:00 AM (06:00) |
| 9:00 AM (09:00) | 7:00 AM (07:00) |
| 10:00 AM (10:00) | 8:00 AM (08:00) |
| 11:00 AM (11:00) | 9:00 AM (09:00) |
| 12:00 PM (12:00) | 10:00 AM (10:00) |
| 1:00 PM (13:00) | 11:00 AM (11:00) |
| 2:00 PM (14:00) | 12:00 PM (12:00) |
| 3:00 PM (15:00) | 1:00 PM (13:00) |
| 4:00 PM (16:00) | 2:00 PM (14:00) |
| 5:00 PM (17:00) | 3:00 PM (15:00) |
| 6:00 PM (18:00) | 4:00 PM (16:00) |
| 7:00 PM (19:00) | 5:00 PM (17:00) |
| 8:00 PM (20:00) | 6:00 PM (18:00) |
| 9:00 PM (21:00) | 7:00 PM (19:00) |
| 10:00 PM (22:00) | 8:00 PM (20:00) |
| 11:00 PM (23:00) | 9:00 PM (21:00) |
Best time to call Denver from Halifax
For most work calls, compare the normal business day in Halifax (AST) with the business day in Denver (MDT). AST commonly covers North America, Caribbean, while MDT is mainly associated with North America.
⚠️ Note: 2026-07-05 is not a normal workday in one or both regions based on their configured calendar. The overlap below should be treated as a reference, not a guaranteed office-hours window.
✅ The most practical overlap on 2026-07-05 is usually 12:00 PM - 5:00 PM AST, which corresponds to 9:00 AM - 2:00 PM MDT. This window sits inside the typical AST workday (9:00 AM - 5:00 PM) and the MDT workday (9:00 AM - 5:00 PM).
- DST Safety: AST or MDT may shift during Daylight Saving Time. Always confirm the converted time for your specific date.
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Frequently Asked Questions
What is the time difference between AST and MDT?
During standard time, Mountain Daylight Time is 2 hours behind Atlantic Standard Time.
Does the Caribbean observe Daylight Saving Time?
The vast majority of Caribbean nations and territories — including Puerto Rico, the Dominican Republic, the US Virgin Islands, Trinidad and Tobago, and Barbados — do not observe Daylight Saving Time and remain on AST (UTC-4) year-round. This means these territories share the same clock as Halifax only during the Atlantic Standard Time window in winter, diverging by one hour once Canada and Bermuda advance to ADT each spring.
What is the difference between AST and ADT?
AST (Atlantic Standard Time) is the standard winter offset at UTC-4:00, observed from the first Sunday in November through the second Sunday in March across all AST regions. ADT (Atlantic Daylight Time) is the summer offset at UTC-3:00, applied by Eastern Canadian provinces and Bermuda when they advance their clocks by one hour during Daylight Saving Time.
When does MDT start and end?
MDT begins on the second Sunday in March at 02:00 local MST time, when clocks spring forward one hour from MST (UTC-7) to MDT (UTC-6). It ends on the first Sunday in November at 02:00 local MDT time, when clocks fall back to MST. In 2026, MDT runs from March 8 through November 1, covering the majority of the calendar year.
Is Arizona on MDT?
Most of Arizona — including Phoenix and Tucson — does not observe Daylight Saving Time and remains on MST (UTC-7) year-round under a state law in effect since 1968, meaning Arizona does not advance to MDT each March. The significant exception is the Navajo Nation, a sovereign territory spanning parts of northeastern Arizona, southeastern Utah, and northwestern New Mexico, which does observe DST and shifts to MDT on the standard federal schedule.