how to get number of days between two dates in php code example

Example 1: php calculate date difference

//get Date diff as intervals 
$d1 = new DateTime("2018-01-10 00:00:00");
$d2 = new DateTime("2019-05-18 01:23:45");
$interval = $d1->diff($d2);
$diffInSeconds = $interval->s; //45
$diffInMinutes = $interval->i; //23
$diffInHours   = $interval->h; //8
$diffInDays    = $interval->d; //21
$diffInMonths  = $interval->m; //4
$diffInYears   = $interval->y; //1

//or get Date difference as total difference
$d1 = strtotime("2018-01-10 00:00:00");
$d2 = strtotime("2019-05-18 01:23:45");
$totalSecondsDiff = abs($d1-$d2); //42600225
$totalMinutesDiff = $totalSecondsDiff/60; //710003.75
$totalHoursDiff   = $totalSecondsDiff/60/60;//11833.39
$totalDaysDiff    = $totalSecondsDiff/60/60/24; //493.05
$totalMonthsDiff  = $totalSecondsDiff/60/60/24/30; //16.43
$totalYearsDiff   = $totalSecondsDiff/60/60/24/365; //1.35

Example 2: Number of week days between two dates in php

You are given two string (dd-mm-yyyy) representing two date, 
you have to find number of all weekdays present in between given dates.
  
function number_of_days($days, $start, $end) {
	$start = strtotime($start); $end = strtotime($end);
	$w = array(date('w', $start), date('w', $end));
	$x = floor(($end-$start)/604800);
	$sum = 0;
	for ($day = 0;$day < 7;++$day) {
		if ($days & pow(2, $day)) {
			$sum += $x + ($w[0] > $w[1]?$w[0] <= $day || $day <= $w[1] : $w[0] <= $day && $day <= $w[1]);
		}
	}
	return $sum;
}

function getWeeklyDayNumbers($startDate, $endDate) {
	$weekdays = array('monday' => 0, 'tuesday' => 0, 'wednesday' => 0, 'thursday' => 0, 'friday' => 0, 'saturday' => 0, 'sunday' => 0);
	$weekdays['monday'] += number_of_days(0x02, $startDate, $endDate); // MONDAY
	$weekdays['tuesday'] += number_of_days(0x04, $startDate, $endDate); // TUESDAY
	$weekdays['wednesday'] += number_of_days(0x08, $startDate, $endDate); // WEDNESDAY
	$weekdays['thursday'] += number_of_days(0x10, $startDate, $endDate); // THURSDAY
	$weekdays['friday'] += number_of_days(0x20, $startDate, $endDate); // FRIDAY
	$weekdays['saturday'] += number_of_days(0x40, $startDate, $endDate); // SATURDAY
	$weekdays['sunday'] += number_of_days(0x01, $startDate, $endDate); // SUNDAY
	return $weekdays;
}

$weekdays = getWeeklyDayNumbers('01-01-2021', '31-01-2021');
print_r($weekdays);exit;