I wish I knew this before my last trip!

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A website called CheapAir.com monitored prices for 4 million flights last year, and found the absolute best time to buy a plane ticket is....exactly 54 days before your trip.

Any earlier than that and you're looking at a higher price, although they say it's generally better to buy earlier than later.

That 54-day mark is for domestic U.S. flights.  If you're going to Mexico, book 89 days in advance....101 days in advance for the Caribbean....129 days in advance for Asia....and 151 days in advance for Europe.

The only time the 54-day window doesn't apply is for Christmas or Thanksgiving flights.  You're best off booking those 6 months before, on June 4th.