No, you cannot use your own United MileagePlus frequent flyer number on a reservation for someone else. A frequent flyer number is strictly tied to the individual traveler's legal name, and it is a violation of the program's terms to attempt to "earn" miles for a flight you are not physically on. If you try to enter your number on a friend's booking, the system will usually reject it because the name on the ticket doesn't match the name on the MileagePlus account. However, you can use your MileagePlus points to book an "Award Flight" for someone else. In this scenario, you log into your account, search for a flight using miles, and during the checkout process, you enter the other person's name and details as the passenger. They will fly for "free" (plus taxes), and you will be the one providing the points. This is a perfectly legal and popular way to share rewards. The traveler will not earn miles on that flight, but they will enjoy the benefits of the ticket you purchased for them. If you have "Elite Status," your benefits (like free checked bags or upgrades) typically do not transfer to the person you booked for unless you are traveling on the same reservation.