If you have a DiscoverIT card, call the number on the back of the card and ask to add the double cash back promotion. You will get 2% cash back for 12 months starting on purchases on your next billing cycle. This is for new and existing customers and you have until July 31. 2015 to enroll.
So how it will work is that at the end of the 12 months, Discover will take all the cash back you have earned and double it and deposit it in the next billing cycle. This goes without saying but if you close your account before the promotion period, you will not get the double cash back.
Also don’t forget to sign up for the 5% cash back this quarter which is at Home Improvement Stores, Department Stores, and Amazon. With the above promotion, you can get 10% cash back (this is unconfirmed), however it is limited to 1,500 in purchases.
I like to raid the gift card racks at the home improvement stores or buy amazon gift cards to maximize this promotion.