[Rick Seaney is the CEO and cofounder of  FareCompareand columnist for Investopedia. The views expressed by columnists are those of the author and do not necessarily reflect the views of Investopedia.]

When it comes to paying for airline tickets, the day of the week you fly matters. There are cheaper and more expensive days, and it all depends on when people like to fly.

In the U.S., people like to fly at Thanksgiving and Christmas, and they like to fly in mid-July, which is why those are usually the most expensive times to purchase airfare. People also like to fly on Fridays and Sundays, which is why those are generally the most expensive days to fly.

Cheapest Days to Fly: U.S. Flights

When to find a deal for domestic travel? Typically by flying on a Tuesday, Wednesday or Saturday.

This is no secret to those who keep up with airline sales. Recent deals from Southwest come with the caveat that sale prices are limited to flights on Tuesday, Wednesday and Saturday, while Frontier frequently offers its super-cheap fares for Tuesday or Wednesday travel only. 

Now for some examples: These April flights from Chicago to Atlanta were found in mid-March on my comparison airfare site. 

The first price is for a ‘cheap days’ itinerary, Wednesday to Tuesday; the second price is for an ‘expensive days’ itinerary, Friday to Sunday.

  • Spirit: $137 vs. $263
  • American: $163 vs. $254
  • United: $163 vs. $320

Bottom line: All the Friday-Sunday flights in this example are significantly more expensive (in some cases, nearly twice the price). For the record, this is not always the case, which is one of the reasons shoppers benefit from using a comparison fare site whenever they book. No single airline always has the best deals, and rules about cheapest days to fly may not be true for every single itinerary.

Cheapest Days to Fly: Europe Flights

This rule is similar but a little looser. Generally, transatlantic flights on weekends are more expensive than transatlantic flights on weekdays. Here’s another example, flights from New York to London in April; the first price is for a week-long itinerary of Wednesday to Thursday, and the second price is for a Saturday-to-Saturday flight. 

  • Iberia: $485 vs. $578
  • British Airways: $552 vs. $877
  • Norwegian: $552 vs. $755
  • Virgin Atlantic: $576 vs. $594

In many cases, flying weekdays can save you a significant amount of money. For example, if you’re a family of four flying British Airways, that’s an extra $1,300 to spend on something fun in the U.K. But what if you’re not especially flexible on your travel dates?

How to Save When Dates Aren’t Very Flexible

First, as noted earlier, always compare fares to see which airlines have the best deal and which days of the week are cheapest.

Second, if you have any flexibility at all, try a domestic itinerary of Saturday to Wednesday. International travelers can price a variety of weekdays to come up with the cheapest plan.

Third, if your days-off are firm – or it’s difficult to fly only on ‘cheap days’ – my advice for both domestic and international travelers is the same: Split the difference. In other words, fly one ‘cheap day’ and one ‘expensive day,’ and you’ll almost always still save something. More examples, based on the two above.

  • Chicago–Atlanta: Fly Friday to Tuesday and the American fare is $212, roughly midway between the ‘cheap days’ price of $163 and the ‘expensive’ price of $254.
  • New York–London: Fly Sunday to Wednesday and the British Airways price is $641, again a compromise price between the extremes of $552 and $877.

Note: These fares were good when I priced them out in mid-March. but airfares are constantly changing. You may or may not find these prices. But knowing the cheapest days to fly will usually save you some money. Sometimes, a whole lot.