Add Date Intervals with PHP

add-date-interval.php

<!-- GATHER INFORMATION FROM FORM -->
<!-- Get date due, the Friday before the week for which the taxi fare applies -->
<?php
/*
 * Create date for testing (due date Friday, 10-13-17)
 */
$monthDue = 10; // $_POST['monthdue'];
$dayDue = 13; // $_POST['daydue'];
$yearDue = 2017; // $_POST['yeardue'];

/*
 * Setup date intervals
 */
$oneDay = new DateInterval('P1D');
$sevenDays = new DateInterval('P7D');

/*
 * Convert date to digital format yyyy-mm-dd
 * Prepend single digit values with zero
 */
if ($monthDue <= 9) {
    $monthDue = 0 . $monthDue;
}
if ($dayDue <= 9) {
    $dayDue = 0 . $dayDue;
}
$dateDueFormatted = $yearDue . '-' . $monthDue . '-' . $dayDue;
$dateDue = date_create($dateDueFormatted);

echo "Due date (\$date): " . $dateDue->format('Y-m-d');
?>
<br/>
<!-- Add one day to due date (Saturday date, start of taxi fare week) -->
<?php
$dateStart = $dateDue->add($oneDay);

echo "Start date: " . $dateStart->format('Y-m-d');
?>
<br/>
<!-- Add seven days to due date (Next Friday's date, End of taxi fare week) -->
<?php
$dateEnd = $dateStart->add($sevenDays);
echo "End date: " . $dateEnd->format('Y-m-d');
?>
<br/>