United Airlines and Chase have refreshed a small-business version of the airline’s co-branded credit card with a generous limited-time sign-up bonus. Learn More Until March 18, the United℠ Explorer Business Card is offering the following Limited Time Offer: Earn 75,000 bonus miles after you spend $5,000 on purchases in the first 3 months your account is... Gregory Karp is a writer at NerdWallet.