public function addMonth($count = 1) { if (!$this->checkTimestamp($this->toTimeStamp() + self::monthsToSeconds($count))) { return; } $month = $this->getMonth() + $count; $day = Gpf_Common_DateUtils::daysInMonth($month, $this->getDay(), $this->getYear()); $this->timestamp = $this->maketime($month, $day, $this->getYear()); }