Summer break: The cheapest domestic flights in July and August are usually available 13 to 43 days in advance, with 21 days before departure being the cheapest day on average to book.

The last time I booked a vacation flight, I literally spent over an hour finding the cheapest ticket to Hawaii with two criteria in mind: that it wasn't a red-eye flight, and it only had one layover.

Ideally, you should book a flight to Europe 11 months before your trip to get the lowest fare, says Jeff Klee, former CEO of CheapAir.com, which monitored fares for more than 4 million flights to ...