If you’ve always thought that Tuesday was the best day of the week to book a cheap flight, think again!

The lowest average ticket price is generally found on Sunday for both economy and premium fares, according to the ARC 2018 Air Travel Outlook Report.

The study is a collaboration between Expedia and the Airlines Reporting Corporation.

RELATED: Use this packing trick to avoid a checked bag fee

Travel alert: Tuesday is NOT always the best time to buy a cheap airline ticket

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 are booked on a Sunday. Friday is 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 results in cheaper fares.

Be flexible with your departure date: Thursday and Friday are the cheapest departure dates for international economy flights. The best day to depart varies by origin for domestic economy flights.

Most/least expensive months: June has the highest average ticket prices for economy travel within the U.S. and September has the lowest prices.

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Clark’s travel tips 

If you’ve been following money expert Clark Howard for a while, you know that his #1 rule of cheap travel is to buy a deal first and then figure out why you want to go there.

That’s why Clark likes to use Kayak Explore to see a map of where the best deals are!

“The more flexible you are and the more spontaneous you are about where you go, the more money you’re going to save,” Clark says.

Not flexible with the destination or dates? In that case, track prices frequently using Google Flights and Southwest.com.

“If you’re really cheap, you try every day of the week and write down the price each day you check,” Clark says. “Learn the pattern and you’ll know when you’ve found your deal.”

Fares tend to be at their lowest about six weeks out from travel, according to Clark.

One thing to keep in mind: Pay close attention any time you’re doing a fare search and looking at one of the three full-fare airlines. The cheap fare you see may be a gotcha!

Read Clark’s warning about American, Delta and United’s cheap fares.

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

Another way to save is to pay attention to the sales. We have the latest travel deals at ClarkDeals.com!