If you missed your flight with United Airlines, then the airline allows you to rebook your flight or use a standby option, which allows you to travel on the same dates. However, you have to pay a certain amount to do so. Further, if the delay was caused by the airline, then according to the United Missed Flight policy, rebooking is usually free of cost. Visit the official website of United Airlines or read the blog mentioned earlier to avail more details on this.