BusinessDateTime, a class that allows you to do simple math for business days.

businessdatetime.php

<?php

class BusinessDateTime extends DateTime
{
    private $holidays = []; // Array to store holidays

    // Constructor
    public function __construct($time = "now", DateTimeZone $timezone = null)
    {
        parent::__construct($time, $timezone);
        $this->setDefaultHolidays(); // Preload default US holidays
    }

    /**
     * Modify the DateTime according to business day rules.
     *
     * @param string $modifier The modifier string (e.g., "+2 business days").
     * @return DateTime|false
     */
    public function modify(string $modifier): DateTime|false
    {
        if (preg_match('/^([\+\-]?\d+)\s*business days?$/i', $modifier, $matches)) {
            return $this->addBusinessDays((int)$matches[1]);
        }

        return parent::modify($modifier);
    }

    /**
     * Add business days to the current date.
     *
     * @param int $businessDays The number of business days to add (can be negative).
     * @return $this
     */
    private function addBusinessDays(int $businessDays): self
    {
        $direction = $businessDays > 0 ? 1 : -1;
        $absDays = abs($businessDays);

        while ($absDays > 0) {
            $this->modify(($direction === 1 ? '+1 day' : '-1 day'));
            if ($this->isBusinessDay()) {
                $absDays--;
            }
        }

        return $this;
    }

    /**
     * Check if the current date is a business day.
     *
     * @return bool
     */
    private function isBusinessDay(): bool
    {
        // Check if the current day is a weekend
        if (in_array($this->format('N'), [6, 7])) {
            return false;
        }

        // Check if the current date is a holiday
        if ($this->isHoliday()) {
            return false;
        }

        return true;
    }

    /**
     * Check if the current date is a holiday.
     *
     * @return bool
     */
    private function isHoliday(): bool
    {
        $year = (int)$this->format('Y');
        $month = (int)$this->format('n');
        $day = (int)$this->format('j');

        // Define holidays using rules instead of fixed dates
        return $this->checkFixedHolidays($year, $month, $day) ||
               $this->checkVariableHolidays($year, $month, $day);
    }

    /**
     * Define fixed holidays.
     */
    private function checkFixedHolidays($year, $month, $day): bool
    {
        $fixedHolidays = [
            '01-01', // New Year's Day
            '07-04', // Independence Day
            '11-11', // Veterans Day
            '12-25', // Christmas Day
        ];

        return in_array(sprintf('%02d-%02d', $month, $day), $fixedHolidays);
    }

    /**
     * Define variable holidays.
     */
    private function checkVariableHolidays($year, $month, $day): bool
    {
        // Variable holidays logic
        // Note: This is simplified and may require adjustments for holiday observances
        // Martin Luther King Jr. Day (Third Monday of January)
        if ($month === 1 && $day >= 15 && $this->format('N') == 1) {
            return true;
        }

        // Presidents' Day (Third Monday of February)
        if ($month === 2 && $day >= 15 && $this->format('N') == 1) {
            return true;
        }

        // Memorial Day (Last Monday of May)
        if ($month === 5 && $day > 24 && $this->format('N') == 1) {
            $lastMonday = (int)$this->format('j') - ((int)$this->format('j') % 7);
            return $lastMonday === 31;
        }

        // Labor Day (First Monday of September)
        if ($month === 9 && $day <= 7 && $this->format('N') == 1) {
            return true;
        }

        // Columbus Day (Second Monday of October)
        if ($month === 10 && $day >= 8 && $this->format('N') == 1) {
            return true;
        }

        // Thanksgiving Day (Fourth Thursday of November)
        if ($month === 11 && $day >= 22 && $this->format('N') == 4) {
            return true;
        }

        return false;
    }

    /**
     * Set the holidays for the current object.
     *
     * @param array $holidays Array of holiday dates in 'Y-m-d' format.
     */
    public function setHolidays(array $holidays): void
    {
        $this->holidays = $holidays; // This method isn't strictly necessary anymore
    }

    /**
     * Retrieve current holidays.
     *
     * @return array
     */
    public function getHolidays(): array
    {
        return $this->holidays; // This method isn't strictly necessary anymore
    }

    /**
     * Set default holidays for the US.
     */
    private function setDefaultHolidays(): void
    {
        // The default holidays will be handled in the isHoliday check
    }
}

examples.php

<?php

require_once __DIR__ . '/businessdatetime.php';

$businessDateTime = new BusinessDateTime();
echo $businessDateTime->format('Y-m-d'); // Current date
$businessDateTime->modify('+12 business days');
echo $businessDateTime->format('Y-m-d'); // 12 business days later