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GMT vs. BST: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on November 3, 2023
GMT (Greenwich Mean Time) is the mean solar time at the Prime Meridian; BST (British Summer Time) is GMT+1, used in the UK during summer.

Key Differences

GMT, or Greenwich Mean Time, represents the mean solar time at the Royal Observatory in Greenwich, London. It was formerly used as the international civil time standard, now superseded in that function by Coordinated Universal Time (UTC). BST, or British Summer Time, is the practice of setting the clocks forward by one hour from GMT during the warmer months, and setting them back by the same amount in the cooler months.
GMT serves as a baseline from which other time zones around the world are set. It is essentially UTC+0. BST, on the other hand, is UTC+1. This means that during the period BST is observed, the UK is 1 hour ahead of GMT.
Both GMT and BST have significant historical and cultural impacts. GMT has long been a standard for scheduling in international contexts. BST, however, was introduced during World War I to save energy, with the idea being that people would have more daylight in the evening and thus reduce the need for artificial lighting.
While GMT remains constant throughout the year, BST changes. This means that in the UK, for part of the year (usually from the last Sunday in March to the last Sunday in October), BST is observed, and for the rest of the year, GMT is in use.
To further complicate matters, not all countries that use GMT as a basis for their time observe a form of daylight saving like BST. Therefore, while GMT can be seen as a constant, BST is a regional adaptation.

Comparison Chart


Mean solar time at the Prime Meridian.
GMT+1, observed during UK's summer.

Relation to UTC



Constant throughout the year.
Part of the year in the UK.

Historical Context

International civil time standard.
Introduced to save energy in WWI.

Global Adaptation

Basis for other time zones.
Specific to regions observing DST.

GMT and BST Definitions


A constant time reference unaffected by Daylight Saving Time.
Even when countries adjust their clocks, GMT remains the same.


The UK's adaptation of Daylight Saving Time.
Don't forget to adjust your clocks for BST.


A time system originally referring to mean solar time at the Greenwich Meridian.
GMT is often used in international contexts.


The time descriptor for the UK between the last Sunday of March and the last Sunday of October.
International meetings with the UK get tricky during BST.


The baseline from which other time zones are set globally.
New York operates at GMT-5 during Standard Time.


A system to save energy by better aligning daylight hours with daily activities.
BST ensures we make the most out of the daylight during summer.


The time zone descriptor for areas that don't observe Daylight Saving Time when it's in effect elsewhere.
Iceland uses GMT all year round.


A regional time adjustment observed in the UK and some other places.
Ireland also observes a form of BST during its summer months.


The mean solar time at the Royal Observatory in Greenwich, London.
The conference call was scheduled for 3 PM GMT.


British Summer Time, which is one hour ahead of GMT.
We switch to BST in March to enjoy longer evenings.


The local time at the 0 meridian passing through Greenwich, England; it is the same everywhere


When is BST observed?

Typically from the last Sunday in March to the last Sunday in October in the UK.

What does GMT stand for?

Greenwich Mean Time.

How is GMT determined?

It's the mean solar time at the Royal Observatory in Greenwich, London.

Are GMT and UTC the same?

Practically, yes, but GMT is based on the Earth's rotation while UTC is based on atomic clocks.

How much time difference exists between GMT and BST?

BST is one hour ahead of GMT.

What does BST stand for?

British Summer Time.

When was GMT established?

GMT was established in the 19th century as the world's time standard.

What's the main purpose of BST?

To make better use of daylight during the summer months in the UK.

Is GMT affected by Daylight Saving Time?

No, GMT remains constant year-round.

Why was BST introduced?

To save energy during World War I by making better use of daylight.

Are there other versions of BST worldwide?

Yes, many countries have their own versions of Daylight Saving Time.

Does the entire world use GMT?

No, GMT serves as a baseline; different regions have their own time zones relative to GMT.

Does the US use GMT?

The US uses time zones based on GMT but doesn't refer to any as GMT.

How can I convert GMT to BST?

Add one hour to GMT to get BST during the months BST is observed.

Why is GMT important in aviation?

GMT provides a consistent time reference for global flight operations.

When do we switch back from BST to GMT?

On the last Sunday in October in the UK.

Is BST the same as Daylight Saving Time?

BST is the UK's version of Daylight Saving Time.

Does every country adjust for Daylight Saving like BST?

No, the adoption of Daylight Saving varies by country.

Which countries observe BST?

The UK and a few other regions observe BST.

Does BST impact international business?

Yes, businesses must account for the hour difference with the UK during BST.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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