Which zone this page means. GMT and UTC are the same offset but not the same thing: GMT is a time zone, UTC is a time standard. The United Kingdom is on GMT in winter and BST (UTC+1) in summer. Japan does not observe daylight saving, so JST applies all year.
GMT is behind JST by 9 hours today
On 19 August 2026, Greenwich Mean Time is on GMT at UTC+00:00 and Japan Standard Time is on JST at UTC+09:00. The gap between them is 9 hours, with JST ahead. So 9:00 am in GMT is 6:00 pm in JST, and 5:00 pm in GMT is 2:00 am in JST. Going the other way, see JST to GMT.
The gap is not constant, and that is the part that catches people out
Neither zone observes daylight saving, so this is one of the few pairs where the offset really is constant all year. That is unusual: most gaps between named zones move by an hour twice a year, and by two hours during the weeks when the two ends change on different dates.
When you can actually both be at work
Taking a working day as 9:00 am to 5:00 pm local at each end, there are 0 overlapping hours in a normal day. There is none: the two working days do not touch at all, so any live meeting between Greenwich Mean Time and Japan Standard Time has to sit outside somebody's normal hours. The table above shows which end has the shorter stretch to give up.
Zone rules are set by legislation and change, sometimes at short notice. This page is built against tzdata 2026a, last reviewed 2026-08-18. Quarterly. Zone rules change by legislation, sometimes at short notice. Version and review date are shown on every zone page. The converter above reads your browser's own copy of the zone database, so if a rule has changed since this page was built the live answer follows the new rule.
Every convention used above — whether the start date counts, how month ends are clamped, which holidays close an office — is written out on the methodology page, including the daylight-saving rules behind the 9-hour gap above.