World Timezones

MST to AST-ATLANTIC Converter

Compare AST-ATLANTIC to MST instead
Mountain Time10:35 pmThu, Jun 4
Mountain TimeMDT
North America · UTC-6
10:35 pmThu, Jun 4
12a
1a
2a
3a
4a
5a
6a
7a
8a
9a
10a
11a
12p
1p
2p
3p
4p
5p
6p
7p
8p
9p
10p
11p
Atlantic TimeADT
North America · UTC-3
1:35 amFri, Jun 5
3a
4a
5a
6a
7a
8a
9a
10a
11a
12p
1p
2p
3p
4p
5p
6p
7p
8p
9p
10p
11p
12a
1a
2a

Offset

The time difference between Mountain Time and Atlantic Time is 3 hours.

3 hours

Mountain Time (MDT) is behind Atlantic Time (ADT).

MDT: UTC-6

ADT: UTC-3

Both zones are currently observing daylight saving time.

When to schedule

Business-hours overlap: 9 AM–2 PM in Mountain Time (12 PM–5 PM in Atlantic Time).

Both teams are in working hours during this window on weekdays.

Suggested time: 11:00 AM Mountain Time (2:00 PM Atlantic Time).

This window may shift by an hour during daylight saving time.

Public holidays in 2026

National public holidays can affect availability — a counterpart is likely off work on their own holidays, so it's worth planning meetings and deadlines around them.

United States

  • New Year's DayThu, Jan 1
  • Martin Luther King, Jr. DayMon, Jan 19
  • Presidents DayMon, Feb 16
  • Memorial DayMon, May 25
  • Juneteenth National Independence DayFri, Jun 19
  • Independence DayFri, Jul 3
  • Labour DayMon, Sep 7
  • Columbus DayMon, Oct 12
  • Veterans DayWed, Nov 11
  • Thanksgiving DayThu, Nov 26
  • Christmas DayFri, Dec 25

Canada

  • New Year's DayThu, Jan 1
  • Good FridayFri, Apr 3
  • Victoria DayMon, May 18
  • Canada DayWed, Jul 1
  • Labour DayMon, Sep 7
  • National Day for Truth and ReconciliationWed, Sep 30
  • ThanksgivingMon, Oct 12
  • Christmas DayFri, Dec 25

About these zones

Mountain Time is also known as MST, or MDT. To call United States, dial +1.

Atlantic Time is also known as AST, or ADT. To call Canada, dial +1.

Atlantic Time is approximately 2,100 miles northeast of Mountain Time.

Quick reference

Full 24-hour conversion table — tap any time to open it in the converter.

MSTAST-ATLANTICDay
12:00 am3:00 amSame day
1:00 am4:00 amSame day
2:00 am5:00 amSame day
3:00 am6:00 amSame day
4:00 am7:00 amSame day
5:00 am8:00 amSame day
6:00 am9:00 amSame day
7:00 am10:00 amSame day
8:00 am11:00 amSame day
9:00 am12:00 pmSame day
10:00 am1:00 pmSame day
11:00 am2:00 pmSame day
12:00 pm3:00 pmSame day
1:00 pm4:00 pmSame day
2:00 pm5:00 pmSame day
3:00 pm6:00 pmSame day
4:00 pm7:00 pmSame day
5:00 pm8:00 pmSame day
6:00 pm9:00 pmSame day
7:00 pm10:00 pmSame day
8:00 pm11:00 pmSame day
9:00 pm12:00 am+1 day
10:00 pm1:00 am+1 day
11:00 pm2:00 am+1 day

Daylight saving time

Both Mountain Time and Atlantic Time observe daylight saving time and transition on the same date.

Next transition: Sunday, November 1, 2026 (fall back).

Because they transition simultaneously, the offset between these zones remains constant year-round.

See the daylight saving time page for transition dates across every time zone.

Daylight today

Mountain Time
Sunrise
5:34 AM
Sunset
8:25 PM
Day length
14h 51m
Atlantic Time
Sunrise
5:31 AM
Sunset
8:56 PM
Day length
15h 25m

Cities in these zones

Cities in Mountain Time

Cities in Atlantic Time

Browse all cities to see the current local time anywhere.

Airports in these zones

Airports in Mountain Time

  • BJC
  • DEN
  • OGD
  • SLC

Airports in Atlantic Time

  • YHZ

Related conversions

Common conversions

What is 9:00 am MST in AST-ATLANTIC?
9:00 am MST is 12:00 pm AST-ATLANTIC.
What is 12:00 pm MST in AST-ATLANTIC?
12:00 pm MST is 3:00 pm AST-ATLANTIC.
What is 12:30 pm MST in AST-ATLANTIC?
12:30 pm MST is 3:30 pm AST-ATLANTIC.
What is 2:00 pm MST in AST-ATLANTIC?
2:00 pm MST is 5:00 pm AST-ATLANTIC.
What is 5:00 pm MST in AST-ATLANTIC?
5:00 pm MST is 8:00 pm AST-ATLANTIC.
What is 11:30 pm MST in AST-ATLANTIC?
11:30 pm MST is 2:30 am AST-ATLANTIC, the next day.