Function: Get date offset accounting for weekends and holidays

dev_script_get_date_offset.php

<?php

// Requires PHP 5.4+
function getWorkingDaysFrom($start, $amtOfDays) {

	$globalDays = 0; // a global addition to $amtOfDays (such as a minimum shipping time of 3 days across all objects)
	$amtOfDays = $amtOfDays + $globalDays; // set base amount of days for initial range before calculations applied
	$ignore = array('6', '7'); // days of the week to ignore (weekends are 6 & 7) in ISO-8061
	$holidays = array(
		(new DateTime('first monday of january +1 year'))->format('*-m-d'), // new years day (celebrated)
		'*-02-29',
		(new DateTime('last monday of may'))->format('*-m-d'), // memorial day
		'*-07-04',
		(new DateTime('first monday of september'))->format('*-m-d'), // labor day
		(new DateTime('fourth thursday of november'))->format('*-m-d'), // thanksgiving
		'*-12-25'
	); // holiday dates (holidays are ignored if they fall into ignore list)

	$oneDay = new DateInterval('P1D');
	$from = new DateTime($start);
	$to = new DateTime($start);

	$to->add(new DateInterval('P' . $amtOfDays . 'D'));

	foreach(new DatePeriod($from, $oneDay, $to) as $day) {	
		if (in_array($day->format('N'), $ignore)) {
			$to->add($oneDay);
		} elseif (in_array($day->format('*-m-d'), $holidays)) {
			$to->add($oneDay);
		}
		while (in_array($to->format('N'), $ignore) || (!in_array($to->format('N'), $ignore) && in_array($to->format('*-m-d'), $holidays))) {
			$to->add($oneDay);
		}
	}

	return $to->format('Y-m-d'); // returns a date (or you can format as $to if you need an object)
}