Understanding JST and UTC
JST stands for Japan Standard Time, UTC+9, used in Japan. UTC stands for Coordinated Universal Time, UTC+0, used in Global time standard. These are specific offset definitions, not automatic substitutes for the local time in a city.
How do you convert JST to UTC?
Subtract the source offset from the destination offset: 0 − (540) = -540 minutes. Subtract 540 minutes from the JST time. For example, 9:00 AM JST is 12:00 AM UTC (same day). If the result crosses midnight, the calendar day changes too.
Does daylight saving time change this conversion?
The difference between these named offsets is fixed. A location may switch to a different abbreviation during daylight saving time, so an invitation saying “EST” can differ from the actual summer time in New York.
Japan uses JST year-round and does not observe daylight saving time.
UTC is the reference for time-zone offsets and does not observe daylight saving time.
Which day does the converted time fall on?
“Previous day” means the destination is one calendar day before the source; “Next day” means one day after. Dates are relative to the day of your input time. A time-only conversion cannot determine a specific calendar date.