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(And here's the most expensive time.)

This article originally appeared on Hopper.com and Money. Hopper is a travel app that tracks and predicts airfare prices. 

It’s popular advice we’ve all read on one site or another: Book early in the morning for the cheapest flights! Or don’t book on a Friday night! Or only book at noon on a Tuesday. Or only book during a full moon. (Okay, that one we haven’t actually heard, but we’re sure someone, somewhere, has decreed it.) So we were curious: Does the time of day you buy your flight really matter? Are certain times of day cheaper? In the name of science, we dove into a whole lot of data (namely, about 20 million separate flight searches over the course of four months) and mapped what we found.

The short answer is yes, the time of day you book kind of matters. The longer answer is, but not really.

Here’s what we found.

Tuesday Around Midnight is the Cheapest Time to Book

We found that travelers who search for flights on Tuesday at midnight save about 6% on their flights, making this the cheapest time of the week to book. In general, flights were slightly cheaper at midnight earlier in the week (Monday through Wednesday). However, this is only applicable to about 1.6% of U.S. markets, meaning that it’s not likely you’ll find the same savings on your specific route. And midnight later in the week actually gets more expensive. So put the “always book at midnight” myth to bed.

Friday Around 3 A.M. is the Most Expensive Time to Book

Hopper did find that shoppers pay about 3% higher fares on Fridays at around 3 A.M. This variation is probably due to the way airlines manage their sales, often starting early in the work week and ending before the weekend. So prices may, in fact, spike a little bit before the weekend kicks off. This travel legend does hold (somewhat) true: Avoid booking late at night later in the week.

Every Route is Different

As the chart above shows, there really is no one-size-fits-all when it comes to the cheapest time of day to book, simply because there are so many factors: airline yield management, airfare sales, demand, and so forth. While some airfares seem to consistently increase at the same time each day, other routes’ prices remain steady throughout the day and week. So anyone who says Tuesday morning is always cheapest may only be looking at a handful of routes.

So What Does Matter When Booking Flights?

First, the day you book: In a previous study Hopper found that the cheapest day to book your flight is Thursday for both domestic and international flights. However, there’s a big caveat: The savings are smaller than you may think: about $10 for typical domestic routes and about $25 for international markets. Much like time of day, every route is different, and contrary to popular belief, there is, once again, no one-size-fits-all approach.

So perhaps more important are the days you fly: Hopper found that the cheapest day to depart, on average, is Wednesday, while the most expensive day is Sunday. The same applies for the day you return: The best day to return from a domestic trip is Tuesday, while the best day to return from an international trip is Wednesday. You’re looking at average savings of $85 (domestic) and $120 (international) by flying out and back on the right days!

Is It Worth It?

If all of the conflicting travel advice you find online has given you hives, you may wonder, does it even matter when I book? Is the agony of searching on different days and times of day even worth it? You may say no, giving up forever on finding the cheapest flights.

You’re welcome, world.

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