The Discover it® Miles credit card will give you an opportunity to redeem miles with any airline, including Virgin America and United Airlines. Miles are earned on every dollar you spend. There is no standard sign-up bonus offered but all miles you earn first year will be matched dollar-for-dollar at the end of the year. So in fact there is no frames on how big your first year bonus can be. There are no caps on how many miles you can earn and miles do not expire. Also, there is no annual fee and you won’t need to pay interest on purchases during first year. After that a regular APR will apply.