Difference Between GMT and BST: Greenwich Mean Time vs British Summer Time

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GMT versus BST

What is the key difference between GMT and BST? Which one is a standard time and which one is a daylight-saving time? Learn all about these timekeeping abbreviations in the following sections that give a detailed comparative study of GMT vs BST.

Greenwich Mean Time (GMT) and British Summer Time (BST) are commonly used timekeeping abbreviations in the United Kingdom. GMT has been in use for more than a century now. The use of BST has been on and off.

Related: What is the Difference Between EST and EDT

GMT vs BST Difference  

What is Greenwich Mean Time (GMT)?

Greenwich Mean Time is a time zone followed in UK, Iceland and in a few countries of Africa.

As you know, the whole world in divided into various time zones according to their local sunrise and sunset times. USA has six time zones like Pacific Standard Time, Eastern Standard Time and so on. Similarly UK has a single time zone which is GMT in the winter and BST in summer.

See: Difference Between East Coast and West Coast: East Coast vs West Coast

History of GMT

Britain was a shipping leader in the 18th century. During one naval expedition Britain lost 1400 men due to incorrect coordinate calculation. This led to people actively seeking the solution to the problem of longitudes.

At that time Royal Observatory at Greenwich was already established. It had a pendulum clock that showed the solar time at Greenwich. It was mostly used by star gazers.

The problem of longitudes was solved when mariners found out that they could accurately calculate their coordinates at sea when they kept one chronometer set to the GMT. This was possible because GMT showed the time at zero degree longitude i.e. the prime meridian.

Soon after, the Railways followed and started using GMT as their standard time for time tables.

Because of its high accuracy, GMT became a standard time all throughout the United Kingdom. Other countries followed suit and started recognizing GMT as the international standard time. The time zones were represented as an offset of GMT like GMT + 1, GMT – 5 and so on.

The international time standard today is UTC and not GMT. This change came into effect from 1972. Now, GMT is a time zone and UTC is a time standard. The time zones are represented as UTC – 2:00, UTC + 1:00 and so on. GMT is UTC + 0.

Read: Difference Between EST and MST: EST vs MST

What is British Summer Time (BST)?

BST is followed in the United Kingdom during the summer months. It is UTC + 1. It is mainly done to take advantage of the evening sunlight and to conserve energy.

History of BST

BST is one of the aftermaths of the First World War. During the First World War, people realized that they could conserve fuel by setting the clocks an hour ahead during the summer time. The first ones to do so were the Germans, with the English following suit.

During the Second World War, British started using double summer time. They would keep their clocks on BST during the winters and on BST + 1 during the summers.

From 1968 to 1971, UK was on BST permanently as a part of Daylight saving experiment. But the experiment failed after it was found that more accidents happened in the darker morning hours.

Since then, UK has been on GMT during winter and on BST only during summer, hence the name British Summer Time.

Clocks change at 1 a.m. Computers, digital watches make the change automatically. But if you have an analog clock, then do not forget to reset the time before you go to sleep to avoid confusion in the morning.

Must See: Difference Between Eastern Time and Pacific Time

Difference Between GMT and BST

Here are some key differences between GMT and BST:

GMT BST
UTC offset UTC + 0 UTC + 1
Countries affected United Kingdom, Republic of Ireland, Iceland, Ghana, Mali and other countries in Africa United Kingdom, Jersey, Isle of Man, Guernsey
Starting time Last Sunday of October Last Sunday of March
Ending time Last Sunday of March Last Sunday of October

People use the phrase “spring forward and fall back” to help them remember to make changes to their clocks during the spring and fall seasons.

Wrapping it up: GMT vs BST Difference

GMT is a time zone followed in many countries. Some countries like Iceland remain on GMT the whole year. Other countries change to daylight saving time during the summer months.

When UK changes from GMT to daylight saving, it is on BST.

Do not forget to change your clocks as and when required. To change your clock from GMT to BST you need to move it ahead by one hour. To change your clock from BST to GMT, you will need to move it back by one hour.

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