Convert JST (Japan Standard Time) to MDT (Mountain Daylight Time)

Best time to schedule a meeting

Standard 9–5 working hours do not overlap at all between JST and MDT. Someone has to take an early or late call — or use asynchronous communication instead.

JST to MDT 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 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 15-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.

JST does not shift, so the whole change comes from one side. A recurring meeting fixed in JST 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