Although it’s impossible to guarantee when travelers will find the lowest fares, the data scientists at ARC and Expedia used trends to identity the best times to book a trip.

Here’s a summary of the key findings to help you save money:

  • Search for low fares on the weekend: The cheapest fares for domestic economy and international economy flights were booked on a Sunday. Friday was the most expensive day of the week to book.
  • It pays to book your flight early: For most economy and premium air travel, booking more than 30 days in advance often resulted in cheaper fares. Don’t wait until the last-minute!
  • Be flexible with your departure date: Thursday and Friday were the cheapest departure dates for international economy flights. The best day to depart varied widely by origin for domestic economy flights.
  • Most/least expensive months: June had the highest average ticket prices for economy travel within the U.S. and September had the lowest prices.

Some travelers say the #1 rule of cheap travel is to buy a deal first and then figure out why you want to go there!

No matter what this report or any other study finds, you can’t go wrong by following the sales.

“Though there are generally better days than others to find great prices on travel, one way to find the best deals is to pay attention to the sales,” said Charis Brown of ClarkDeals.com. “Airlines often take advantage of #TravelTuesday to offer airfare deals, in conjunction with the social media hashtag. You’ll save the most by taking a look at sales and deals as often as possible!”

Finally, have you heard about Scott’s Cheap Flights? You can sign up for either a free or paid subscription and have cheap flight deals delivered to your inbox all the time.