PHP get start and end date of a week by weeknumber

We can achieve this easily without the need for extra computations apart from those inherent to the DateTime class.

function getStartAndEndDate($year, $week)
{
   return [
      (new DateTime())->setISODate($year, $week)->format('Y-m-d'), //start date
      (new DateTime())->setISODate($year, $week, 7)->format('Y-m-d') //end date
   ];
}

The setISODate() function takes three arguments: $year, $week, and $day respectively, where $day defaults to 1 - the first day of the week. We therefore pass 7 to get the exact date of the 7th day of the $week.

Slightly neater solution, using the "[year]W[week][day]" strtotime format:

function getStartAndEndDate($week, $year) {
  // Adding leading zeros for weeks 1 - 9.
  $date_string = $year . 'W' . sprintf('%02d', $week);
  $return[0] = date('Y-n-j', strtotime($date_string));
  $return[1] = date('Y-n-j', strtotime($date_string . '7'));
  return $return;
}

Using DateTime class:

function getStartAndEndDate($week, $year) {
  $dto = new DateTime();
  $dto->setISODate($year, $week);
  $ret['week_start'] = $dto->format('Y-m-d');
  $dto->modify('+6 days');
  $ret['week_end'] = $dto->format('Y-m-d');
  return $ret;
}

$week_array = getStartAndEndDate(52,2013);
print_r($week_array);

Returns:

Array
(
    [week_start] => 2013-12-23
    [week_end] => 2013-12-29
)

Explained:

• Create a new DateTime object which defaults to now()
• Call setISODate to change object to first day of $week of $year instead of now()
• Format date as 'Y-m-d' and put in $ret['week_start']
• Modify the object by adding 6 days, which will be the end of $week
• Format date as 'Y-m-d' and put in $ret['week_end']

A shorter version (works in >= php5.3):

function getStartAndEndDate($week, $year) {
  $dto = new DateTime();
  $ret['week_start'] = $dto->setISODate($year, $week)->format('Y-m-d');
  $ret['week_end'] = $dto->modify('+6 days')->format('Y-m-d');
  return $ret;
}

Could be shortened with class member access on instantiation in >= php5.4.

Many years ago, I found this function:

function getStartAndEndDate($week, $year) {
  $dto = new DateTime();
  $dto->setISODate($year, $week);
  $ret['week_start'] = $dto->format('Y-m-d');
  $dto->modify('+6 days');
  $ret['week_end'] = $dto->format('Y-m-d');
  return $ret;
}

$week_array = getStartAndEndDate(52,2013);
print_r($week_array);