public function getDeltaDays($from, $to, $timezone = 'user')
    {
        $dtFrom = $this->toDateTime($from, $timezone);
        $dtTo = $this->toDateTime($to, $timezone);
        if (is_null($dtFrom) || is_null($dtTo)) {
            return null;
        }

        // Re-create DateTime objects without time
        $dtFrom = $this->toDateTime($dtFrom->format('Y-m-d'), $timezone);
        $dtTo = $this->toDateTime($dtTo->format('Y-m-d'), $timezone);

        return (int) $dtFrom->diff($dtTo)->format('%r%a');
    }