What time zone does GMT use?
GMT is the standard time in the United Kingdom during winter months. But here’s the thing: the UK observes Daylight Saving Time (DST), so from late March to late October, the clocks jump forward to British Summer Time (BST), which is UTC+1. So if you’re planning a call in summer, don’t rely on GMT — it’s BST then.
UTC offset and DST change dates for 2026
In 2026, the UK switches to BST (UTC+1) on March 29 at 1:00 AM GMT, when clocks spring forward to 2:00 AM. Then on October 25 at 2:00 AM BST, they fall back to 1:00 AM GMT. So for most of the year, the offset is +1, not zero. Keep that in mind if you’re scheduling anything across the pond.
Best times for international calls
Let’s say you’re in London. For New York (typically UTC-5 or -4), the best overlap is 2:00 PM to 4:00 PM GMT/BST, which is 9:00 AM to 11:00 AM Eastern. For Tokyo (UTC+9), aim for 8:00 AM to 10:00 AM GMT/BST — that’ll be late afternoon for them, around 4:00 PM to 6:00 PM. Sydney (UTC+11) gets tricky: your 9:00 AM is their 7:00 PM in winter, but in summer it’s 8:00 PM. So early morning calls work best.
Business hours overlap with major markets
If you’re doing business, London’s standard 9:00–5:00 overlaps nicely with New York’s morning, so you get a solid 3–4 hour window. With Tokyo, you’ve got a narrow 1–2 hour window in the late afternoon if you push your day. And Sydney? Almost no overlap during UK office hours — you’re looking at early morning or late evening. Plan accordingly.
Fun fact about GMT
Here’s a mind-bender: Greenwich Mean Time was originally based on the mean solar time at the Royal Observatory in Greenwich, London. But since 1972, it’s been replaced by Coordinated Universal Time (UTC) as the global standard. Yet the UK keeps using the name GMT out of tradition. So technically, GMT is now just a time zone, not the reference for world time anymore. Still gets all the glory though!