BST Time Converter: London to US Time

The model, stated exactly

London time is Europe/London: BST (British Summer Time, UTC+1) from the last Sunday in March at 01:00 GMT to the last Sunday in October at 02:00 BST, and GMT (UTC+0) the rest of the year. This converter never hand-rolls those offsets: it resolves the entered London wall time to a UTC instant by iterating the platform's Europe/London zone data, then reads UTC and every US zone from that same instant. US zones are Eastern (UTC−4 EDT / UTC−5 EST), Central (UTC−5 CDT / UTC−6 CST), Mountain (UTC−6 MDT / UTC−7 MST), and Pacific (UTC−7 PDT / UTC−8 PST), each on its own daylight saving calendar. Because both ends are read from real zone data, the converter is right on changeover Sundays too, not just on ordinary days.

The worked example, line by line

Setup: 12:00 on October 24, 2026, the day before the clocks go back, when London is still on BST.

Line 1 — London zone. October 24 is before the last Sunday of October, so London is on BST, UTC+1.

Line 2 — UTC. 12:00 − 1 hour = 11:00 UTC on October 24.

Line 3 — Eastern. 11:00 UTC − 4 hours (EDT) = 07:00 EDT on October 24.

Line 4 — Central. 11:00 UTC − 5 hours (CDT) = 06:00 CDT on October 24.

Line 5 — Mountain. 11:00 UTC − 6 hours (MDT) = 05:00 MDT on October 24.

Line 6 — Pacific. 11:00 UTC − 7 hours (PDT) = 04:00 PDT on October 24.

Try these

Winter: 12:00 on January 15, 2026. London is on GMT, so UTC is 12:00, and the US has fallen back: 07:00 EST Eastern, 06:00 CST Central, 05:00 MST Mountain, and 04:00 PST Pacific, all on January 15. Note that the US times look the same as in October even though London moved — because the US moved too, by the same hour, a week later.

The day after the change: 12:00 on October 25, 2026. The clocks went back at 02:00 BST to 01:00 GMT, so noon is now 12:00 UTC, and the US times are 08:00 EDT, 07:00 CDT, 06:00 MDT, and 05:00 PDT — every US time one hour later than the day before, because London fell back while the US had not yet.

The week the zones disagree. London falls back on the last Sunday in October, but the US falls back a week later, on the first Sunday in November. For that one week the London-to-Eastern gap is 4 hours instead of 5, and a recurring meeting set by London time lands an hour earlier in the US than it did all summer. Enter both Sundays' dates to see the shift before it surprises you.

Spring forward: 12:00 on March 29, 2026. The last Sunday in March is the day London springs forward, so noon is already 11:00 UTC and 07:00 EDT — while the day before, March 28, noon London time was 12:00 UTC. A meeting that straddles the London changeover shifts by an hour even though nothing changed in the US.

Output · formula · meaning

Who uses this

• The remote worker with a London team: enters the London meeting time and date, and stops joining an hour early or late in the changeover weeks.
• The traveller landing at Heathrow: converts the flight arrival time before leaving home, so the hotel pickup is booked for the right London hour.
• The family calling relatives in the UK: checks whether evening at home is a polite morning hour in London or an unwelcome middle-of-the-night one, before dialling.
• The scheduler setting a recurring call: tests a summer date, a winter date, and both changeover Sundays, and writes the invite with the seasonal times spelled out.

Accuracy & limitations

The conversion is exact for the entered date and time, because both the London and US zones are read from the platform's zone data rather than from fixed offsets. Two edge cases deserve a note. First, on the fall-back Sunday (October 25, 2026), the hour from 01:00 to 02:00 happens twice in London; the converter reads the first occurrence, on BST, which is the natural reading for a scheduled time. Second, on the spring-forward Sunday (March 29, 2026), the hour from 01:00 to 02:00 does not exist in London, and a time entered in that gap is resolved to the nearest valid reading — do not schedule a call in that hour. This is a converter, not a live clock: it converts the time you enter and does not track the current time. Error policy: malformed or out-of-range dates and times, and calendar dates that do not exist, are reported as errors rather than converted.