Ticket prices tend to be highest on Fridays, especially if you’re booking a flight less than three weeks in advance, according to the Wall Street Journal citing a new study by Expedia.

While leisure travelers are more likely to book their flights over the weekend, it’s common for businesspeople to wait until the end of the workweek to book their upcoming travel. Air travelers would save the most if they could hold out until the weekend, when airlines are more likely to list inexpensive fares that business travelers won’t grab.

Though it’s long been conventional wisdom to book flights on Tuesdays, since sales tend to be posted at the beginning of the week, that’s no longer a sure bet. Now fares are adjusted all the time, and sales are often just for unpopular flights or offered in targeted social media campaigns.

A more effective scrimping strategy than booking by days of the week is to book early. The lowest-priced economy tickets for flights within North America were sold 57 days in advance, according to the Journal. For trips from North America to Europe, it’s best to buy almost a half-year—176 days—ahead.

There is some good news for all travelers, despite the frustration of constantly changing fares: Expedia says that prices have been dropping. Already, global airfares in October were 8% down from the same month last year. That’s primarily thanks to cheap oil and budget airlines increasing the size of their fleets.