Traveling is expensive. Add a flight into the mix and sometimes the trip cost is so high you wonder if you should just forget about it altogether. Watching flight prices can get tiresome and you may get nervous prices will go up if you don't book soon. If only there was a magic number of days prior to your flight that guaranteed you the lowest fare. While it's not a perfect system, Reader's Digest featured an article in which CEO of CheapAir, Jeff Klee, reveals the "sweet spot" to get the cheapest rates: 70 days before your trip.

After analyzing over 917 million fares, CheapAir has several points of advice on when to buy your airfare. The most obvious? Don't wait until the last minute. The company points out that it rarely works out and you can be stuck paying an exorbitant amount for your flight, especially once it's only 20 days out. On the opposite end of the spectrum, don't book too early. Between 320 and 106 days before a flight, prices tend to stay relatively constant. After that, they usually start dropping, with the peak of the drop around 70 days.

So while there's no magic number set in stone, the data does give some helpful tips to keep in mind the next time you're buying a plane ticket.