It’s easy to find recommendations telling you when to book your flight, but these recommendations span anywhere from 2 weeks to 6 months. The discrepancy probably arises from a statistical problem: seasonal anomalies break the average, and it’s not an easy problem to fix. For example, it will never be cheaper to book 1 week in advance in mid-December because mid-to-late December are the most expensive times to fly. A raw average cannot account for this problem.

Champion Traveler analyzed over 200,000 flight path prices. These trips account for nearly all flights leaving from or departing to the United States, plus the vast majority of international flights (estimated at 80%). We ran the prices multiple times throughout the year, then adjusted for seasonality before saying for sure when you should book your flight. Here’s what we found.

  • To be safe, book domestic flights at least 3.5 weeks (24 days) into the future, but at least 2.5 weeks (18 days) out. During this time closer dates will be more expensive in most cases. Booking 0-2 days out will cost quite a bit more: sometimes as much as 2 times as much. A week or so in advance is usually not too bad at an average 10% markup, but flights that are not flown often can still cost 40% more if they’re even available.
  • Internationally prices don’t fluctuate as much, but you should still book international flights at least 1 week in advance. International flights are more heavily impacted by seasonality, fill up farther in advance, and obviously cost more. But if you don’t mind taking the red-eye flights no one else wanted, you may be able to find a regular price on short notice.
  • Avoid booking more than 9 months in advance for domestic flights, and 10 months in advance for international flights. Why the charge for planning in advance? The reason airlines give is that this is a “fixed plan” fee. Airlines may change routes or times, and there are always costs with moving passengers around. There’s also a cost to ensuring you can fly on the date and around the times you specified. Sometimes airlines change flight paths, and they will be obligated to find you a new flight (sometimes not even with their own airline) if their plans change.
  • Unsurprisingly, you can expect to pay much more booking a flight on the day of the flight. Most passengers who buy tickets this late have emergencies, and are expecting to be over-charged. There are very few exceptions to the rule, but some flights are much cheaper on the day of or a few days before. These are flights where passengers cancel or a flight is under-sold. As frequent travelers know, this is extremely rare because most airlines over-book every flight expecting a few people to miss the flight.

There’s generally no downside to booking in advance, provided the trip is less than 9 months out. Not only do the best flights (e.g. those 11 AM flights that aren’t too early and aren’t too late) still have space, but the prices aren’t likely to go up very much. Click the link below to find current prices and book a flight.

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Prices Graphed by Weeks in the Future (May Example)

These graphs are typical examples for ticket prices for a flier looking at tickets in the middle of May. These graphs show the (non-seasonally adjusted) average price for foreign and domestic flights by day. In the example the price rise in the near future is the summer vacation spike. June to August is almost always more expensive. The second price spike is for travelers around the holiday season, especially in late December around Christmas, Hanukkah, and New Year. The third and final price spike is for booking too far in advance. Also visible are the daily spikes for the weekend, with the low points being Tuesday and the high points being Sunday. For more on that, see the cheapest times to fly.

May Example: Flying Domestic

May Example: Flying International

As you can see, a passenger looking for a flight in May would have little control of prices during peak times: summer vacations, holidays, etc. But most of the time you can at least plan on avoiding buying airline tickets very near in the future or very far away. For more info on pricing make sure to read our guide to the cheapest times to fly.

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