Detect BST in php

I am building a booking system in php that offers session times for people to book outdoor activities.

In the summer months, there is an extra session available at the end of the day, because of Daylight Savings, there is an extra hour in the evenings.

Year    Clocks go forward   Clocks go back
2014    30 March            26 October
2015    29 March            25 October
2016    27 March            30 October
2017    27 March            30 October
2018    25 March            28 October

I am using this…

$todaysDate = strtotime(date("Y-m-d"));
$bstBegin = strtotime("2015-03-29");
$bstEnd = strtotime("2015-10-25");

if($todaysDate > $bstBegin && $todaysDate > $bstEnd)
{
   echo "<option value="evening">Evening Session</option>";
}

I only need to show this extra option in the select list between these dates. Is this something I will need to set manually from year to year, or is there a PHP date variable that knows the days the clocks change?

Answer

$today = strtotime(date("Y-m-d"));
if (date('I', $today)) {
    echo "We're in BST!";
} else {
    echo "We're not in BST!";
}

or use the DateTime object equivalent, which maintains details of all the transition dates globally