Unused gift cards abound.  United now lets you convert those cards into frequent flyer miles with their MileagePlus Gift Card Exchange Program.  Just visit the airline’s website’s “trade gift card” section to initiate the exchange process. For every $25 in gift card value, members receive 670 United MileagePlus miles.   The process is entirely digital, eliminating the need to mail physical gift cards. Just select the merchant’s name from a list of participating retailers and enter the card’s balance. The system then presents an offer detailing the miles available in exchange for the card’s value. Once accepted, the transaction is typically processed immediately, though some may take up to five business days to complete.  There are no exchange limits, you can trade an unlimited number of gift cards although it is still important to evaluate the exchange rate. Depending on the gift card’s value, it might be more cost-effective to use it for its original purpose or sell it through other platforms.