What is the time difference between JST and MST?

Mountain Standard Time (MST) is 15 hours behind Japan Standard Time (JST). JST uses a UTC offset of UTC+9, while MST uses UTC-6. For example, when it's 9:00 AM in JST, it's 6:00 PM in MST. Note that this difference may shift by one hour during daylight saving time transitions if MST observes DST. Use the conversion table above to see the exact time for each hour of the day.

How do I convert JST to MST?

To convert JST to MST, subtract 15 hours from the JST time. For example, 9:00 AM JST is 6:00 PM MST, and 5:00 PM JST is 2:00 AM MST. Keep in mind that during daylight saving time transitions, the offset between these timezones may temporarily change by one hour. You can also use the interactive converter above for quick, accurate results.

What time is it in MST when it's noon in JST?

When it's 12:00 PM (noon) in JST, it's 9:00 PM in MST. This is because MST is 15 hours behind JST. Similarly, when it's 6:00 PM in JST, it's 3:00 AM in MST. During daylight saving time transitions, these times may shift by one hour, so always verify the current offset. The color-coded conversion table above shows every hour mapped between both timezones.

How many hours behind is MST from JST?

MST is 15 hours behind JST. This means when it's 9:00 AM in JST, it's 6:00 PM in MST, and when it's midnight in JST, it's 9:00 AM in MST. The exact difference can vary by one hour during daylight saving time transitions. The conversion table above provides a complete hour-by-hour mapping.

Is MST ahead or behind JST?

MST is behind JST by 15 hours. Clocks in MST show an earlier time than JST, meaning the day starts later in MST relative to JST. For example, when it's noon in JST, it's still 9:00 PM in MST. This gap may change by one hour during DST transitions.

Does JST observe daylight saving time?

No, Japan Standard Time does not observe daylight saving time. The UTC offset of UTC+9 remains the same year-round, making time conversions from JST more predictable. Countries and regions in this timezone keep their clocks unchanged regardless of the season.

Does MST observe daylight saving time?

Yes, Mountain Standard Time observes daylight saving time. During DST, the abbreviation changes to MDT and clocks move forward by one hour, typically in spring. Clocks then fall back in autumn, returning to standard MST time. This means the UTC offset for MST shifts between two values depending on the season. Check our DST change calendar for exact transition dates that may affect your JST to MST conversions.

What is the best time to call from JST to MST?

The best time for a call between JST and MST is during overlapping business hours (9 AM – 5 PM) in both timezones. To reach someone in MST during their work day, call between 12:00 AM and 8:00 AM your JST time. Avoid calling too early or late, as the 15 hours difference means your evening could be their early morning. Check the color-coded conversion table above — green hours indicate business hours in both zones, making it easy to find the ideal time.

When does daylight saving time change in MST?

Daylight saving time transitions vary by year and region. Mountain Standard Time observes DST, which typically shifts clocks forward by one hour in spring ("spring forward") and back in fall ("fall back"). During these transition periods, the time difference between JST and MST may temporarily change by one hour, which can cause confusion for scheduled meetings or calls. It's important to double-check your conversions around transition dates, especially if the two timezones switch on different dates. Check our DST change calendar for exact transition dates in the current year.

Do JST and MST ever have the same time?

No, JST and MST never show the same time because their base UTC offsets are different. However, because MST observes daylight saving time and JST does not, the time difference between them changes by one hour during DST transitions. This means the gap narrows or widens depending on the season, but the two clocks never align. Always verify the current offset around DST transition dates to avoid scheduling errors.

JST to MST Converter

Convert Japan Standard Time to Mountain Standard Time. See the hour-by-hour conversion table below.

Timezone Details

Japan Standard Time

6:45 PM

Friday, April 3, 2026

JST (UTC+09:00)

Mountain Standard Time

3:45 AM

Friday, April 3, 2026

MDT (UTC-06:00)

Difference: -15 hours

JST DST: No

MDT DST: Yes (MDT)

24-Hour Overview

JST — 24-hour overview

12a12a

3a3a

6a6a

9a9a

10a

11a

12p12p

3p3p

6p6p

9p9p

10p

11p

NightMorningBusinessEvening

MDT — 24-hour overview

9a9a

10a

11a

12p12p

3p3p

6p6p

9p9p

10p

11p

12a12a

3a3a

6a6a

NightMorningBusinessEvening

Frequently Asked Questions

Related Conversions

MST to JST EST to JST JST to EST PST to JST JST to PST GMT to JST JST to GMT IST to JST JST to IST

Cities in These Timezones

JST Cities

Tokyo Osaka Fukuoka

MST Cities

Denver

More Tools

Compare JST & MST Plan a Meeting (JST & MST)See on Map

Learn More

How Time Zones Work Understanding DST Timezone Abbreviations

External Resources

Japan Standard Time on Wikipedia Mountain Standard Time on Wikipedia IANA Time Zone Database