JST vs MST time zone comparison

How JST and MST compare

Japan Standard Time (JST) sits at UTC+09:00 today, while Mountain Standard Time (MST) is at UTC-06:00. The current gap is 15 hours, with JST ahead of MST. In practical terms, if your morning starts at 9 AM in Tokyo, your counterpart in Denver is seeing 18:00 on their own watch at that exact moment.

JST is the working clock for Tokyo, Osaka and Yokohama. MST covers Denver. If your team is split between these two regions, the table above is the quickest way to spot the daily overlap window without doing the offset arithmetic in your head.

Daylight saving matters here. Japan Standard Time does not change. Mountain Standard Time also shifts seasonally, so the gap between the two zones can move by an hour twice a year. The IANA tzdata baked into this page handles every transition automatically, so the table reflects the correct wall-clock times for today's date. For dates further out, use the converter linked above and pick the target date explicitly.

Common scheduling traps are easy to avoid here. Pick a wall-clock time on one side, read the matching wall-clock on the other from the table, and write both into the calendar invite, never just the difference. If the meeting falls in the week of a DST changeover and one of these zones shifts, the absolute clock will drift by an hour from what the recipient expects. The table is computed for today's date, so for a future meeting open the converter linked above and pick the exact date.

One last note for asynchronous teams: business-hour overlap is the wrong metric for handoff workflows. If you operate on a follow-the-sun model, you actually want zero overlap, with one team logging off as the other starts. JST and MST differ by 15 hours, which gives you partial coverage. Add a zone in between if you want full 24-hour rotation.