Yes, you can use your United MileagePlus miles to upgrade a flight for someone else, even if you are not traveling with them on the same itinerary. This process is typically handled through a "MileagePlus Upgrade Award." To do this, you simply log into your United account, locate the recipient's reservation using their confirmation number and last name, and select the "Redeem Upgrade" option. The number of miles required depends on the fare class purchased and the region of travel; additionally, some lower-priced economy fares may require a "co-pay" in cash alongside the miles. It is important to note that the upgrade is subject to "R" class availability, which is the specific inventory United sets aside for upgrades. If an upgrade is not immediately available, you can place the traveler on a waitlist. If the waitlist does not clear, the miles and any co-pay will be refunded to your account. This is a popular way for frequent flyers to gift premium experiences to friends or family. For those with Premier status, you can also use your PlusPoints to upgrade others following a similar logic, providing even more flexibility for sharing your hard-earned benefits with loved ones.