Convert JST to AST

AST is 13 hours behind JST. JST is UTC+9 and AST is UTC−4.

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 do not overlap at all between JST and AST. Someone has to take an early or late call — or use asynchronous communication instead.

JST to AST conversion table

About JST

Japan Standard Time (JST) is UTC+9. It is used in all of Japan, with no daylight saving.

Japan Standard Time is UTC+9 for the whole country and has had no daylight saving since 1951, when the occupation-era experiment was abandoned. Proposals to reintroduce it, most recently before the 2020 Olympics, have failed each time. The offset is shared with South Korea, so Tokyo and Seoul never differ by even a minute.

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.

Does this gap change with the seasons?

Neither JST nor AST shifts with the seasons, so this 13-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 JST conversions

• JST to UTC
• JST to GMT
• JST to EST
• JST to EDT
• JST to CST
• JST to CDT
• JST to MST
• JST to MDT
• JST to PST
• JST to PDT
• JST to AKST
• JST to HST
• JST to BRT
• JST to BST
• JST to CET
• JST to CEST

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