How to retrieve date from table cell using PhpSpreadsheet?

The value is amount of days passed since 1900. You can use the PhpSpreadsheet built-in functions to convert it to a unix timestamp:

$value = $worksheet->getCell('A1')->getValue();
$date = \PhpOffice\PhpSpreadsheet\Shared\Date::excelToTimestamp($value);

Or to a PHP DateTime object:

$value = $worksheet->getCell('A1')->getValue();
$date = \PhpOffice\PhpSpreadsheet\Shared\Date::excelToDateTimeObject($value);

I hope my answer will complete for those who are lost with reading date. I also had an issue with a column containing dates. When I read in Excel all dates were at the format d/m/Y, but using PhpOffice\PhpSpreadsheet, some lines were read as d/m/Y and others as m/d/Y. Here is how I do:

First, I check the format with ->getDataType()

my default format is m/d/Y but when ->getDataType() returns 's' it becomes d/m/Y

$cellDataType = $objSheetData->getCell("D".$i)->getDataType();
$cellFormat = 'm/d/Y';
if ($cellDataType=='s'){
    $cellFormat = 'd/m/Y';
}
$resultDate=\DateTime::createFromFormat($cellFormat, $sheetData[$i]['D']);

it works fine

When we are iterating with $row->getCellIterator() or we might have other kinds of value, it might be useful to use getFormattedValue instead

while using getValue()

• Full name: Jane Doe => "Jane Doe"
• DOB: 11/18/2000 => 36848.0

while using getFormattedValue()

• Full name: Jane Doe => "Jane Doe"
• DOB: 11/18/2000 => "11/18/2000"

Since i cant add comment just adding an answer for future users. you can convert a excel timestamp to unix timestamp by using the following code (from accepted answer)

 $value = $worksheet->getCell('A1')->getValue();
 $date = \PhpOffice\PhpSpreadsheet\Shared\Date::excelToTimestamp($value);

And you can determine whether the given cell is Date Time using \PhpOffice\PhpSpreadsheet\Shared\Date::isDateTime($cell) function.