Flying Blue Sells Miles With Up to an 80% Bonus, but a Devaluation Lands Mid-Sale

Flying Blue is selling miles with up to an 80 percent bonus through September 16, but there is a big catch: Air France and KLM awards get more expensive on September 8, right in the middle of the sale.

• The offer: Buy Flying Blue miles and earn a bonus, up to 80 percent. You need to buy at least 4,000 miles for the 50 percent bonus, and at least 25,000 miles to reach the full 80 percent.
• The catch, and it is a real one: On September 8, Air France and KLM awards move to Light, Standard, and Flex tiers, and the cheapest tier strips lounge access, changes, and the free checked bag. Miles you buy today may not go as far after that date.
• Only buy for a booking you have lined up: Buy miles only if you have a specific Flying Blue award ready to lock in, ideally before September 8. Do not stock up speculatively.
• Where it shines: Flying Blue is one of the better ways to reach Europe in business class from the East Coast.

If you have a Europe trip ready to book before September 8, the bonus lowers what those miles cost you. If not, this is one to skip.