Convert AST to UTC

UTC is 4 hours ahead of AST. AST is UTC−4 and UTC is UTC+0.

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 4 hours: 9:00 AM–1:00 PM AST (1:00 PM–5:00 PM UTC). Schedule meetings inside that window.

AST to UTC 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 UTC

Coordinated Universal Time (UTC) is UTC+0. It is used in the global time standard, used by aviation, computing and science.

UTC is not a time zone. It is the reference all the others are defined against, and no country runs its civil clocks on it — the places at UTC+0 are on GMT or WET, which are separate things that happen to agree in winter. It never changes for daylight saving, which is exactly why servers, aviation, and every log file you will ever read are timestamped in it. The one irregularity is the leap second, inserted to keep UTC within a second of the Earth's rotation; the practice is due to be abandoned by 2035.

Does this gap change with the seasons?

Neither AST nor UTC shifts with the seasons, so this 4-hour difference holds all year. That is unusual enough to be worth relying on: most cross-continental gaps move twice a year.

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 GMT
• AST to EST
• AST to CST
• AST to CDT
• AST to MST
• AST to MDT
• 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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