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Daylight Savings Time (referred to in Brazil as horário de verão or, often, simply hora de verão; summer time) starts and ends at midnight on different dates each year. The start and the end dates somewhat coincide with the start of spring and autumn (fall) in the Southern Hemisphere:

Seasons in the Southern Hemisphere
winter—June 22 to September 21
spring—September 22 to December 21
summer—December 22 to March 21
autumn / fall—March 22 to June 21

As in the United States, for example, the old adage "spring forward and fall back" (which pertains to which way to move the clock for the start/end of Daylight Savings Time) can also be applied to Brazil, albeit, taking into account its location in the Southern Hemisphere.

In the past, the start and end dates of horário de verão (summer time / Daylight Savings Time)  were often only announced a week or two before they were to take effect. Now, the official dates for the start and end have been scheduled well in advance:

2010
Ends Saturday, 20 February 2010  ("fall" back 1 hour)
Starts Saturday, 16 October 2010 ("spring" forward 1 hour)

2011
Ends Saturday, 19 February 2011 ("fall" back 1 hour)
Starts Sunday, 16 October 2011 ("spring" forward 1 hour)

2012
Ends Saturday, 25 February 2012 ("fall" back 1 hour)
Starts Sunday, 21 October 2012 ("spring" forward 1 hour)

2013
Ends Saturday, 16 February 2013 ("fall" back 1 hour)
Starts Sunday, 20 October 2013 ("spring" forward 1 hour)

2014
Ends Saturday, 15 February 2014 ("fall" back 1 hour)
Starts Sunday, 19 October 2014 ("spring" forward 1 hour)

2015
Ends Saturday, 21 February 2015 ("fall" back 1 hour)
Starts Sunday, 18 October 2015 ("spring" forward 1 hour)

2016
Ends Saturday, 20 February 2016 ("fall" back 1 hour)
Starts Sunday, 16 October 2016 ("spring" forward 1 hour)

2017
Ends Saturday, 18 February 2017 ("fall" back 1 hour)
Starts Sunday, 15 October 2017 ("spring" forward 1 hour)

2018
Ends Saturday, 17 February 2018 ("fall" back 1 hour)
Starts Sunday, 21 October 2018 ("spring" forward 1 hour)

2019
Ends Saturday, 16 February 2019 ("fall" back 1 hour)
Starts Sunday, 20 October 2019 ("spring" forward 1 hour)