MDT to AST Converter
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Quick answers
Selected conversion
6:00 am06:00 MDT (UTC-6), Oct 18, 2026 = 9:00 am09:00 ADT (UTC-3), Oct 18, 2026
MDT is 3 hours behind ADT.
MDT and AST examples
These examples always use MDT (UTC-6) and AST (UTC-4). They stay the same when you change the date or time above. The selected conversion may differ when daylight saving time applies.
MDT is 2 hours behind AST.
How the time difference changes
For most of the year, MDT is 3 hours behind ADT. From Nov 1, 2026 to Mar 14, 2027, MST is 3 hours behind AST. Briefly around clock changes, MDT is 2 hours behind AST or MST is 4 hours behind ADT.
For most of the year, working hours of 9:00 am to 6:00 pm in MDT correspond to 12:00 pm to 9:00 pm in ADT. At other times of the year, working hours of 9:00 am to 6:00 pm in MST correspond to 12:00 pm to 9:00 pm in AST.For most of the year, working hours of 09:00 to 18:00 in MDT correspond to 12:00 to 21:00 in ADT. At other times of the year, working hours of 09:00 to 18:00 in MST correspond to 12:00 to 21:00 in AST.
Compare MDT time with AST time, including current local time, UTC offsets, time difference, daylight saving changes, working hours, and shareable meeting times.
Time Difference
Mountain Daylight Time is 3 hours behind Atlantic Daylight Time.
6:00 am06:00 in MDT is 9:00 am09:00 in ADT
MDT to ADT call time
Best time for a conference call or a meeting is between 9am-3pm09:00-15:00 in MDT which corresponds to 12pm-6pm12:00-18:00 in ADT
6:00 am06:00 Mountain Daylight Time (MDT). Offset UTC -6:00 hours
9:00 am09:00 Atlantic Daylight Time (ADT). Offset UTC -3:00 hours
6:00 am06:00 MDT / 9:00 am09:00 ADT
Choose an hour to update the converter. Day labels such as “next day” or “+1” are relative to the selected date in the first column. Use Up and Down arrow keys, Home or End to move between hours, then Enter or Space to select.
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Mountain Daylight Time
Offset: MDT is 6 hours behind Greenwich Mean Time (GMT).
Countries using this time zone: Canada, Mexico, United States
Principal Cities: The largest city in the MDT time zone is Ciudad Juárez in Mexico, with about 1.512 million people. Other major cities in this time zone include Denver, El Paso, Albuquerque, Colorado Springs.
French: HAR - Heure Avancée des Rocheuses
Spanish: MT - Zona Pacífico
Today all shaded areas are on MDT.
Daylight Saving: Mountain Daylight Time (MDT) is a daylight saving/summer time zone. During winter, some places set clocks back one hour and observe Mountain Standard Time (MST).
Start: Mountain Daylight Time (MDT) started on Sunday, March 8, 2026 at 2:00 am02:00 local time and clocks were set one hour forward to Sunday, March 8, 2026, 3:00 am03:00. Daylight saving starts annually on the second Sunday of March.
End: Mountain Daylight Time (MDT) ends on Sunday, November 1, 2026 at 2:00 am02:00 local time and clocks are set one hour back to Sunday, November 1, 2026, 1:00 am01:00 local standard time instead. Daylight saving ends annually on the first Sunday of November.
See USA daylight saving time and upcoming clock changes worldwide.
MDT representations, usage and related time zones
- -06 - basic short
- -0600 - basic
- -06:00 - extended
- -0600 - sign character (-) followed by a four digit time providing hours (06) and minutes (00) of the offset. Indicates an offset of six hours to the west of the zero meridian.
- Sierra - Military abbreviation for MDT
- S - short form of 'Sierra'
- America/Boise
- America/Cambridge_Bay
- America/Ciudad_Juarez
- America/Denver
- America/Edmonton
- America/Inuvik
- America/Shiprock
- America/Yellowknife
- Canada/Mountain
- MST7MDT
- Navajo
- US/Mountain
- CST - Central Standard Time
- CT - Central Time
- MDT - Mountain Daylight Time
- EAST - Easter Island Standard Time
- GALT - Galapagos Time
- S - Sierra Time Zone
Atlantic Standard Time
Offset: AST is 4 hours behind Greenwich Mean Time (GMT).
Countries using this time zone: Anguilla, Antigua and Barbuda, Aruba, Barbados, Bermuda, British Virgin Islands, Canada, Caribbean Netherlands, Curaçao, Dominica, Dominican Republic, Greenland, Grenada, Guadeloupe, Martinique, Montserrat, Puerto Rico, Saint Barthélemy, Saint Kitts and Nevis, Saint Lucia, Saint Martin, Saint Vincent and the Grenadines, Sint Maarten, Trinidad and Tobago, US Virgin Islands
Principal Cities: The largest city in the AST time zone is Santo Domingo in the Dominican Republic, with about 2.202 million people. Other major cities in this time zone include Santiago de los Caballeros, Halifax, San Juan, San Pedro de Macorís.
French: HNA - Heure Normale de l'Atlantique
Spanish: AST - Tiempo Estándar del Atlántico
Today the lighter areas are on UTC−3 (ADT).
Daylight Saving: This is a standard time zone. During summer, some places set clocks forward one hour for daylight saving time and observe Atlantic Daylight Time (ADT).
End: Atlantic Standard Time (AST) ended on Sunday, March 8, 2026 at 2:00 am02:00 local time and clocks were set one hour forward to Sunday, March 8, 2026, 3:00 am03:00 local daylight time instead. Standard time ends annually on the second Sunday of March.
Start: Atlantic Standard Time (AST) starts on Sunday, November 1, 2026 at 2:00 am02:00 local time and clocks are set one hour back to Sunday, November 1, 2026, 1:00 am01:00. Standard time starts annually on the first Sunday of November.
See Canada daylight saving time and upcoming clock changes worldwide.
AST representations, usage and related time zones
- -04 - basic short
- -0400 - basic
- -04:00 - extended
- -0400 - sign character (-) followed by a four digit time providing hours (04) and minutes (00) of the offset. Indicates an offset of four hours to the west of the zero meridian.
- Quebec - Military abbreviation for AST
- Q - short form of 'Quebec'
- America/Anguilla
- America/Antigua
- America/Aruba
- America/Barbados
- America/Blanc-Sablon
- America/Curacao
- America/Dominica
- America/Glace_Bay
- America/Goose_Bay
- America/Grenada
- America/Guadeloupe
- America/Halifax
- America/Kralendijk
- America/Lower_Princes
- America/Marigot
- America/Martinique
- America/Moncton
- America/Montserrat
- America/Port_of_Spain
- America/Puerto_Rico
- America/Santo_Domingo
- America/St_Barthelemy
- America/St_Kitts
- America/St_Lucia
- America/St_Thomas
- America/St_Vincent
- America/Thule
- America/Tortola
- America/Virgin
- Atlantic/Bermuda
- Canada/Atlantic
- Atlantic Standard Time - UTC -4
- Arabia Standard Time - UTC +3
- AST - Atlantic Standard Time
- EDT - Eastern Daylight Time
- AMT - Amazon Time
- BOT - Bolivia Time
- CDT - Cuba Daylight Time
- CLT - Chile Standard Time
- GYT - Guyana Time
- HLV - Hora Legal de Venezuela
- Q - Quebec Time Zone
- VET - Venezuelan Standard Time