Convert AST to MDT

MDT is 2 hours behind AST. AST is UTC−4 and MDT is UTC−6.

Which AST is this?

AST names more than one zone. This page reads it as Atlantic Standard Time at UTC−4, which is the reading most converters take. There is one other: Arabia Standard Time at UTC+3, used in Saudi Arabia, Iraq, Kuwait, Bahrain, Qatar and Yemen.

The letters on a meeting invitation do not say which one is meant. If yours is not Atlantic Standard Time, the answer above is wrong, and not by a little:

The large converter sites disagree about this as well: search for a AST conversion and some of the results answer for one reading and some for another, none of them saying which they chose. Where it matters, ask which country the sender is in rather than which letters they typed.

Best time to schedule a meeting

Standard 9–5 working hours overlap for 6 hours: 11:00 AM–5:00 PM AST (9:00 AM–3:00 PM MDT). Schedule meetings inside that window.

AST to MDT conversion table

About AST

Atlantic Standard Time (AST) is UTC−4. It is used in Halifax, Puerto Rico and the eastern Caribbean in winter.

Atlantic Standard Time is UTC−4, one hour ahead of Eastern. It covers Canada's Atlantic provinces, Puerto Rico and much of the eastern Caribbean, and it is the reason a call from Halifax to Toronto is an hour out from what either party expects. The abbreviation is also used for Arabia Standard Time at UTC+3, seven hours away in the other direction, which is a genuinely dangerous collision in scheduling.

About MDT

Mountain Daylight Time (MDT) is UTC−6. It is used in Denver and Salt Lake City from March to November.

Mountain Daylight Time is UTC−6, the summer clock for Denver and Salt Lake City. During those months it coincides with Central Standard Time, which is a genuine source of confusion in a country that spans both: a meeting at "6pm MDT" and one at "6pm CST" are the same instant, but the second is not a time anyone is actually on in summer.

Does this gap change with the seasons?

This gap is seasonal. The abbreviations themselves are fixed offsets, but the region on MDT switches to MST (UTC−7) from November to March. So the 2-hour figure on this page is correct for the part of the year when both places are actually on these abbreviations, and changes by an hour outside it.

AST does not shift, so the whole change comes from one side. A recurring meeting fixed in AST will appear to move by an hour for everyone on the other side, twice a year, without anyone changing anything.

This is the reason scheduling systems store an IANA zone such as Region/City rather than an offset or an abbreviation: the zone knows its own rules and the offset does not.

Frequently asked questions

Other AST conversions

• AST to UTC
• AST to GMT
• AST to EST
• AST to CST
• AST to CDT
• AST to MST
• AST to PST
• AST to PDT
• AST to AKST
• AST to HST
• AST to BRT
• AST to BST
• AST to CET
• AST to CEST
• AST to EET
• AST to EEST

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