Normally, clocks are put forward an hour on the last Sunday in March, and then put back an hour on the last Sunday in October.
In 2016, summer time will last from 27 March to 30 October.
During that time, we move our clocks forward by an hour - so, if you normally get up at 8am, it will feel like 7am.
The change is called 'daylight saving', and the idea is to make the most of natural daylight, by arranging for the hours of the day when we do the most things to happen when it's light.
Starting the day earlier means that mornings are darker, but it stays light for longer in the evenings.
It was first done in the UK in 1916 - 100 years ago - during the First World War.
The aim was to save fuel, and give people more time to work in the fields.
Now, some people think that we should have British Summer Time all year round.

The actor, on his fourth outing as 007 in Spectre, had told Time Out magazine that he would "rather slash [his] wrists" than make a fifth Bond film.
But he told the BBC: "I'm quite straightforward and I say things when I feel it and then I change my mind.
"I'm just like everybody else.  People latch onto things. There's not a lot I can do about that."
Spectre, which is released on Monday, sees Bond battling a criminal syndicate led by Franz Oberhauser, played by Christoph Waltz.
A preview screening in London on Wednesday to film critics and journalists was greeted with applause and cheers.
Among the five-star reviews were the Telegraph's Robbie Collin, who said Spectre combined "hold-your-breath action and ghosts of 007's past".
Speaking to the BBC's Lizo Mzimba on Thursday, Daniel Craig said he and director Sam Mendes had wanted to celebrate Bond but "didn't want to look back and copy what's been done before".
He acknowledged that most Bond fans have a "very particular memory about certain Bond movies" and that it would be "unwise to ignore all of that".
The actor said that having a producing credit on the film was "the high point" of his career.
"I knew when I accepted the role that it would turn my life upside down and it did. There's no getting away from it.
"I'm still enjoying it much more than I ever did because I've been allowed to bring what I know to the role. I've been involved with every aspect of film-making."
Asked if he had made a decision about carrying on as Bond, Craig added: "No - this is what's going on at the moment.  I'm enjoying this."

Daniel Pelka was murdered in Coventry in March 2012 by his mother and her partner.
City council leader Ann Lucas said more children's social workers was "the answer" to the "huge pressures" her staff faced.
The council said cases rose from 3,085 in March 2013 to 4,529 in March 2014.
Ms Lucas said reports of suspected child abuse had increased dramatically since Daniel's death.
The council currently has a team of 197 children's social workers.
But, Ms Lucas said the authority had grown increasingly reliant on agency workers, who were more expensive and did not provide the same consistency on cases.
"We have no choice - we have to take in agency workers," she said. "There aren't enough trained social workers.
"Social workers also have a huge burn-out rate. These people are working at the coal-face.
"I take my hat off to them. I think they are heroes - I don't know why they do it. They are castigated at every turn."
One social worker Chris Horne, told the BBC: "The bottom line is if there's more work than there are social workers, we're always going to struggle."
Senior social worker Sarb Bhambra added: "Staffing is always an issue. It's impossible to manage all the priorities because everything is a priority and there's only so many of us."
A freedom of information request reveals the number of reports of suspected abuse in Coventry has soared by 40% since 2011. There were more than 21,000 in 2013.
The results of an Ofsted inspection of children's services in Coventry are expected to be released in the coming weeks.
At 1am on Easter Sunday, the clocks moved forward by one hour, marking the start of British Summer Time.
[NEXT_CONCEPT]
Daniel Craig has said he has not made any decisions about whether he will carry on playing James Bond.
[NEXT_CONCEPT]
Children's social workers on a council that "missed chances" to save a four-year-old boy's life say they need more staff to cope with rising caseloads.