MST to ADT Converter
Mountain Time is on daylight saving time: MDT (UTC−6) until Sun, Nov 1.
Arizona stays on MST (UTC−7).
Start by searching for a time zone, city, or town.
Add one or more places to compare local times, adjust the date, and share the result.
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.
MST and ADT examples
These examples always use MST (UTC-7) and ADT (UTC-3). They stay the same when you change the date or time above. The selected conversion may differ when daylight saving time applies.
MST is 4 hours behind ADT.
Most of Arizona stays on MST (UTC-7) all year. Places such as Denver use MDT (UTC-6) during daylight saving time, one hour later. For daylight-time examples, use MDT to ADT.
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 MST time with ADT 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 Standard Time
Offset: MST is 7 hours behind Greenwich Mean Time (GMT).
Countries using this time zone: Canada, Mexico, United States
Principal Cities: The largest city in the MST time zone is Phoenix in the United States, with about 1.65 million people. Other major cities in this time zone include Ciudad Juárez, Hermosillo, Culiacán, Denver.
French: HNR - Heure Normale des Rocheuses
Spanish: MT - Zona Pacífico
Today the lighter areas are on UTC−6 (MDT).
Daylight Saving: This is a standard time zone. During summer, some places set clocks forward one hour for daylight saving time and observe Mountain Daylight Time (MDT).
End: Mountain Standard Time (MST) 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: Mountain Standard Time (MST) 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 USA daylight saving time and upcoming clock changes worldwide.
MST representations, usage and related time zones
- -07 - basic short
- -0700 - basic
- -07:00 - extended
- -0700 - sign character (-) followed by a four digit time providing hours (07) and minutes (00) of the offset. Indicates an offset of seven hours to the west of the zero meridian.
- Tango - Military abbreviation for MST
- T - short form of 'Tango'
- America/Boise
- America/Cambridge_Bay
- America/Ciudad_Juarez
- America/Creston
- America/Dawson
- America/Dawson_Creek
- America/Denver
- America/Edmonton
- America/Fort_Nelson
- America/Hermosillo
- America/Inuvik
- America/Mazatlan
- America/Phoenix
- America/Shiprock
- America/Whitehorse
- America/Yellowknife
- Canada/Mountain
- Canada/Yukon
- MST
- MST7MDT
- Mexico/BajaSur
- Navajo
- US/Arizona
- US/Mountain
- MST - Mountain Standard Time
- PDT - Pacific Daylight Time
- YST - Yukon Standard Time
- T - Tango Time Zone
Atlantic Daylight Time
Offset: ADT is 3 hours behind Greenwich Mean Time (GMT).
Countries using this time zone: Bermuda, Canada, Greenland
Principal Cities: The largest city in the ADT time zone is Halifax in Canada, with about 471,559 people. Other major cities in this time zone include Sydney, Moncton, Saint John, Fredericton.
French: HAA - Heure Avancée de l'Atlantique
Today all shaded areas are on ADT.
Daylight Saving: Atlantic Daylight Time (ADT) is a daylight saving/summer time zone. During winter, some places set clocks back one hour and observe Atlantic Standard Time (AST).
Start: Atlantic Daylight Time (ADT) 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: Atlantic Daylight Time (ADT) 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 Canada daylight saving time and upcoming clock changes worldwide.
ADT representations, usage and related time zones
- -03 - basic short
- -0300 - basic
- -03:00 - extended
- -0300 - sign character (-) followed by a four digit time providing hours (03) and minutes (00) of the offset. Indicates an offset of three hours to the west of the zero meridian.
- Papa - Military abbreviation for ADT
- P - short form of 'Papa'
- America/Glace_Bay
- America/Goose_Bay
- America/Halifax
- America/Moncton
- America/Thule
- Atlantic/Bermuda
- Canada/Atlantic
- ADT - Atlantic Daylight Time
- PMT - Pierre & Miquelon Standard Time
- PMST - Pierre & Miquelon Standard Time
- AMST - Amazon Summer Time
- ART - Argentina Time
- BRT - Brasilia Time
- CLST - Chile Summer Time
- FKST - Falkland Islands Summer Time
- FKT - Falkland Islands Time
- GFT - French Guiana Time
- P - Papa Time Zone
- PYST - Paraguay Summer Time
- PYT - Paraguay Time
- SRT - Suriname Time
- UYT - Uruguay Time