In the graph below you see the time zone difference between Greenwich Mean Time and Japan Standard Time. Drag the bubble to adjust the time and to see the corresponding time in the other time zone.
Greenwich Mean Time is the time zone of the 0 meridian, located in London, United Kingdom, including cities like London, Lisbon and Dublin (in the winter). Japan Standard Time is the time zone of Japan, with places like Tokyo, Osaka, Sapporo, Nagoya and Fukuoka.
Usually it is preferable to schedule meetings before lunch for the person in GMT and in the late afternoon for the person in JST.
GMT, or Greenwich Mean Time, is the zero when it comes to time zones – they are all counted from the zero meridian that runs through the village of Greenwich.
While both the UK and Portugal are officially on GMT you need to pay attention to whether they are actually observing it or are using their own. Britain in the summer for example use British Summer Time – which is different than GMT.
London, Lisbon, Dublin, Edinburgh
GMT does not observe DST as it is the zero hour time zone – it never changes.
Japan Standard Time, or JST for short, is the standard time zone of Japan. It is 9 hours ahead of UTC. This also includes the islands of Okinawa even though they previously used a separate time zone. These days all of Japan runs on Japan Standard Time, from Hokkaido to Kyushu.
Japan is the only country using Japan Standard Time. It is however the same time as KST – Korean Standard Time and AWDT – Australian Western Daylight Time (i.e. when Western Australia applies Daylight Saving Time).
All cities in Japan applies JST, including Tokyo, Kyoto, Sapporo, Fukuoka, Hiroshima, Nagano and Nagoya.
DST (Daylight Saving Time) is currently not applied in Japan, although there have been attempts to re-introduce it. Especially the northern island of Hokkaido are in favor of DST as the sun rises very early in summer under the current system. Another argument to re-introduce DST has been that it would have a positive effect on emissions, but this has not been proven in any studies yet.