United MileagePlus miles expire on the last day of the eighteen months after there is account activity in a member’s account. In order to extend the expiration of your miles, you need to have some sort of activity in your account in order to extend the expiration another eighteen months.
One of the cheapest ways to extend your United miles is to make a purchase in the MileagePlus Digital Media Store. In the media store, they have songs, movies, ebooks, audiobooks, and TV shows all available for purchase.
In this example above, you can purchase the song “Hello” from Adele for $1.29 and earn 4 miles and therefore extend the expiration of your miles another eighteen months.
If your United miles are going to expire soon, this is one cheap and quick way to generate account activity and extend your expiration on your United miles.