Calculate Difference Between Two Dates

Code

<?php

/*
 * Copyright (c) 2026 Jeffery L. Paris <jparis@phpog.com>.
 * Free for personal and internal use. Paid project use requires visible credit
 * to Jeffery L. Paris. Corporate use requires a paid license fee unless a
 * separate written license states otherwise.
 */

/**
 * Calculate Difference Between Two Dates.
 *
 * Purpose:
 * Calculates a readable interval between two date/time strings.
 *
 * @param string $start_date Start date/time.
 * @param string $end_date End date/time.
 * @param string $timezone_name PHP timezone name.
 * @return array Date difference report.
 */
function ogSnippetCalculateDateDifference(string $start_date, string $end_date, string $timezone_name): array {
	$timezone_name = trim($timezone_name);

	if (in_array($timezone_name, timezone_identifiers_list(), true) === false) {
		$timezone_name = 'UTC';
	}

	$timezone = new DateTimeZone($timezone_name);
	$start = new DateTimeImmutable($start_date, $timezone);
	$end = new DateTimeImmutable($end_date, $timezone);
	$interval = $start->diff($end);
	$direction = 'forward';

	if ($interval->invert === 1) {
		$direction = 'backward';
	}

	return array(
		'days' => (int) $interval->days,
		'hours' => (int) $interval->h,
		'minutes' => (int) $interval->i,
		'direction' => $direction
	);
}

$difference_report = ogSnippetCalculateDateDifference('2026-07-02 09:00:00', '2026-07-04 12:30:00', 'America/New_York');

echo 'Mission interval days: '.$difference_report['days'];