Convert Atlantic Standard Time to Mountain Daylight Time
Instantly convert Atlantic Standard Time (AST) to Mountain Daylight Time (MDT) with our free online calculator.
Atlantic Standard Time
01:20:59 AM
Wed, Jun 24 (AST)
Mountain Daylight Time
11:20:59 PM
Tue, Jun 23 (MDT)
Convert a Specific Time
24-Hour Comparison
| AST | MDT |
|---|---|
| 12:00 AM | 10:00 PM(-1d) |
| 1:00 AM | 11:00 PM(-1d) |
| 2:00 AM | 12:00 AM |
| 3:00 AM | 1:00 AM |
| 4:00 AM | 2:00 AM |
| 5:00 AM | 3:00 AM |
| 6:00 AM | 4:00 AM |
| 7:00 AM | 5:00 AM |
| 8:00 AM | 6:00 AM |
| 9:00 AM | 7:00 AM |
| 10:00 AM | 8:00 AM |
| 11:00 AM | 9:00 AM |
| 12:00 PM | 10:00 AM |
| 1:00 PM | 11:00 AM |
| 2:00 PM | 12:00 PM |
| 3:00 PM | 1:00 PM |
| 4:00 PM | 2:00 PM |
| 5:00 PM | 3:00 PM |
| 6:00 PM | 4:00 PM |
| 7:00 PM | 5:00 PM |
| 8:00 PM | 6:00 PM |
| 9:00 PM | 7:00 PM |
| 10:00 PM | 8:00 PM |
| 11:00 PM | 9:00 PM |
How to Convert Atlantic Standard Time to Mountain Daylight Time
Formula
To convert Atlantic Standard Time (AST) to Mountain Daylight Time (MDT): Convert AST to MDT
About Atlantic Standard Time (AST)
Atlantic Standard Time (AST, IANA: America/Halifax, America/Puerto_Rico) is the time zone for the Canadian Maritime provinces and most of the Caribbean, set at UTC-4:00. AST is observed in: Nova Scotia, New Brunswick, Prince Edward Island, Labrador (partially), Newfoundland's Labrador portion, eastern Quebec, Puerto Rico, US Virgin Islands, Bermuda, Anguilla, Antigua, Aruba, Barbados, British Virgin Islands, Curaçao, Dominica, Grenada, Guadeloupe, Martinique, Saint Lucia, Saint Vincent, Trinidad and Tobago, and Venezuela (since 2007). Canadian Maritime provinces observe AST in winter and switch to ADT = UTC-3:00 in summer per the Energy Policy Act-aligned Canadian schedule. The Caribbean territories (Puerto Rico, USVI, Bermuda) and US territories observe AST year-round without DST per their territorial governments. AST is the same offset as EDT (Eastern Daylight Time) during US summer months, so Halifax and New York are on the same clock in summer but Halifax is one hour ahead in winter.
About Mountain Daylight Time (MDT)
Mountain Daylight Time (MDT, IANA: America/Denver during DST window) is the summer-time variant of MST, set at UTC-6:00 — observed from the second Sunday in March to the first Sunday in November per the Energy Policy Act of 2005. MDT shares the same UTC offset as Central Standard Time (CST), which can cause cross-time-zone scheduling confusion during the DST transition windows in March and November. The Navajo Nation in northeastern Arizona does observe MDT (unlike the rest of Arizona), creating one of the rare US sub-state time-zone exceptions per the Navajo Nation Council's 1968 resolution. MDT applies in Colorado, Utah, Wyoming, Montana, Idaho east, New Mexico, parts of Texas, and Canadian Rocky Mountain provinces (Alberta, eastern BC). Used in coordination of: Denver International Airport flight operations, ski-area lift hours during shoulder-season DST window, Yellowstone National Park ranger schedules, US National Renewable Energy Lab operations, and FAA Albuquerque ARTCC ATC operations.