United MileagePlus: Buy-Miles Discount Runs Through August 20

United is discounting purchased MileagePlus miles through August 20, but it only pays off if you already have a specific premium-cabin redemption lined up.

• The offer: United is selling MileagePlus miles at a personalized rate through August 20. Offers vary by member; some see a discount (up to about 45% off), others a bonus on the miles they buy. Log in to see your own price.
• The cap: United limits purchases to 50,000 miles every 90 days, bonus included, so you cannot stock up heavily.
• When it is worth it: only if you have a specific award booked or ready to book where United miles shine, like Star Alliance business or first class. For everyday economy, buying miles usually costs more than the ticket is worth, so skip it.
• How: log in at united.com, check your personalized buy-miles price, and buy only the exact amount you need for a booking you are ready to make.