One day, you are going to have to make a decision! You're staring blankly at the flight checkout page: on one hand, you have the credit card in one click and on the other, 'use your miles'! All of a sudden, it feels like you're playing a 'do or die' game of "Choose Your Own Adventure" with those two buttons. One ticket leads to a postcard-perfect tropical paradise dream, whilst the other leads to a mild case of buyer's remorse! The big question is: When should you redeem United miles for cash , and when should you just open your wallet? The short answer: Redeem United miles when the cent-per-mile value goes over your personal threshold (primarily in the vicinity of 1.2-1.5 cents). If the cash price of the flight is peanuts, use cash and hang onto your miles. For a last-minute, business-class flight or perhaps some throne-like arrangements, however, considering taking wings of the miles is fair. Let me break down the math and the strategy fo...