Daylight saving time
Tokyo (Japan) does not change clocks: UTC+9 all year. London (United Kingdom) observes daylight saving time from the last Sunday of March to the last Sunday of October: UTC+0 in January, UTC+1 in July.
London uses GMT (UTC+0) in winter and British Summer Time (BST, UTC+1) in summer.
Best time for a call
If both sides work 9:00–18:00 local time, the shared window is no overlap (9:00 in Tokyo is 00:00 in London) in January and 17:00–18:00 in Tokyo = 09:00–10:00 in London (1 hour) in July. Put recurring calls in this window and state the time with the city name (for example “14:00 Tokyo time”) to avoid confusion. How to schedule a meeting across time zones.
How to read the chart
The left column is the local time in Tokyo, the other columns show the same moment in London in January and in July. “+1 day” means it is already the next calendar day in London, “−1 day” — still the previous one. Rows outside 9:00–18:00 are dimmed. The converter above works the other way too: press “Swap” to enter a time in London.