JST to AST: JST is 12 hours ahead of AST

Japan Standard Time is 12 hours ahead of Atlantic Time right now. It is 4:40 am JST in Japan and 4:40 pm ADT in Atlantic, which is already the previous day there.

Convert a specific time from JST to AST

Pick any time and date to convert it both ways. The conversion runs in your browser against the real zone rules, so a date inside a daylight saving period gets that period's offset rather than today's.

What is the time difference between JST and AST?

Atlantic Time is 12 hours behind Japan Standard Time. To go from JST to AST you subtract 12 hours. That gap is not fixed. Across 2026 the distance between these two zones takes 2 different values, from 12 hours to 13 hours, because Atlantic moves its clocks and Japan does not. This page recomputes it rather than assuming.

JST to AST conversion table

Every hour of Thursday, September 24, 2026 in Japan, with the matching reading in Atlantic. 12 of the 24 hours land on a different calendar date in Atlantic, which is the part people get wrong when they schedule across this pair.

What are the best hours to schedule a call between JST and AST?

No hour of the standard 9:00 am to 5:00 pm working day falls inside working hours on both sides. Japan and Atlantic are 12 hours apart, which is too far for an overlap, so somebody has to take a call outside their own working day. The least painful options are below, ranked by how close both sides sit to the middle of the afternoon.

Does daylight saving change JST to AST?

Japan Standard Time does not move its clocks at all, so its UTC+9 offset holds every day of the year.

Atlantic Time is currently on ADT and changes next on Sunday, November 1, 2026, when the clock falls back from 1:59 am to 1:00 am and the offset moves from UTC-3 to UTC-4.

Because the two sides do not move together, the answer to this conversion changes during the year. For part of the year the gap is 12 hours and for the rest it is 13 hours. The table above is built for today, not for an average day.

Is JST ahead of or behind AST?

JST is ahead of AST by 12 hours: when it is 12:00 pm in Japan, it is 12:00 am in Atlantic. One wrinkle worth knowing: AST and ADT are two names for the same zone, not two zones. Atlantic Time reads AST in winter and ADT in summer. When somebody types "jst to ast" they nearly always mean the zone rather than the literal winter offset, so this page resolves JST to Asia/Tokyo and AST to America/Halifax and applies whichever offset is genuinely in force on the day.

Japan Standard Time covers Tokyo, Osaka and the whole of Japan. Atlantic Time covers Halifax, Moncton and the Canadian Maritimes. The identifiers behind them are Asia/Tokyo and America/Halifax, which is what any calendar or scheduling system should be storing rather than a fixed number of hours.

Questions

What is JST in AST?

JST is 12 hours ahead of AST. 9:00 am JST is 9:00 pm the previous day AST.

How many hours ahead is AST of JST?

AST is 12 hours behind JST. That varies across the year, between 12 hours and 13 hours.

What time is it in Atlantic right now?

4:40 pm ADT on Wednesday, September 23, 2026.

When can Japan and Atlantic meet during working hours?

There is no shared working hour. The closest fit is 7:00 am JST, which is 7:00 pm AST.

Does this account for daylight saving?

Yes. Every reading is computed from the IANA database for the actual date, so JST and ADT are the abbreviations genuinely in force today rather than a fixed assumption.

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