BST Time Zone Converter

What BST means

BST stands for British Summer Time and it is exactly one hour ahead of GMT, i.e. UTC+1. It runs during the British summer; the rest of the year the UK is on GMT (UTC+0). The United Kingdom has used the zone continuously since 1968, and the IANA identifier for it is "Europe/London" — a single zone that flips between two abbreviations.

One piece of genuine British terminology to watch out for: the UK government calls the winter time "Greenwich Mean Time" and the summer time "British Summer Time". "British Standard Time" is a colloquialism that many people use for the winter clocks, but it is not the official name and it can cause confusion when a colleague abroad says "BST" meaning "British Standard Time" instead.

When BST starts and ends

Clocks go forward on the last Sunday in March at 01:00 GMT, jumping straight to 02:00 BST — so that night is only 23 hours long. Clocks go back on the last Sunday in October at 02:00 BST, returning to 01:00 GMT, giving a 25-hour day. Any scheduled call that lands between 01:00 and 02:00 on those two dates needs special care.

Because the switch happens on the last Sunday rather than a fixed date, the exact date shifts every year. A converter that hardcodes "the last Sunday in March" is fine; a converter that hardcodes "March 29" is not. This one reads the rule from the IANA database, so it is right every year without maintenance.

BST vs IST: the two meanings people mix up

Ireland uses the same clocks as the UK but calls its summer time Irish Standard Time (IST), also UTC+1 — and it is on IST right now, alongside London. That is the closest and most common mix-up.

The other IST is Indian Standard Time (UTC+5:30), used in Delhi, Mumbai and Chennai. It has nothing to do with summer time at all — India has no daylight saving — and it sits six and a half hours ahead of BST. Whenever you see "IST" in an email, check the sender's country before assuming.

• London in summer (BST, UTC+1) → New York in summer (EDT, UTC−4): 5 hours behind
• London in winter (GMT, UTC+0) → New York in winter (EST, UTC−5): 5 hours behind
• London in summer → Berlin in summer (CEST, UTC+2): 1 hour behind
• London in summer → Dubai (UTC+4): 3 hours behind
• London in summer → Delhi (UTC+5:30): 4:30 hours behind
• London in summer → Tokyo (UTC+9): 8 hours behind

Why UK time changes catch people out

The gap between London and New York is five hours all year, but the reason changes twice: in winter it is GMT versus EST, and in summer it is BST versus EDT. That makes the offset stable while the labels move, which is easy to forget when you are reading a spreadsheet of meeting times.

The larger shock is the swing against the United States, which changes on the first Sunday in November rather than the last Sunday in October. For about a week the UK is on GMT while the US is already on EST, so the gap between London and New York briefly becomes six hours before settling back to five. Australia and New Zealand swing the other way in the southern hemisphere, which shifts the London–Sydney gap from 9 to 11 hours twice a year.