By Grace Elkus
Updated December 15, 2015
A stack of cash on a calandar
Credit: Nick M Do / Getty Images

Buying plane tickets can often feel like a (stressful) game of chance. Do you purchase them on the spot, or wait a few days to see if the price drops? Do you listen to your friend who swears by buying her tickets on Tuesdays?

As it turns out, there are certain days that tend to have the best deals—and also days where ticket prices spike. According to Expedia's 2016 Air Travel Outlook report, which examined data from 10 million tickets and and 300,000 unique routes from 2015, weekends are usually the best time to buy domestic flights, with Sundays tending to have slightly cheaper flights than Saturdays. The next best option? Tuesdays, followed closely by Wednesdays. The report was created in partnership with the Airlines Reporting Corporation.

The day to avoid is Friday, when ticket prices were, on average, 11 percent higher than on Sundays. But it's not all about the day of the week. For the best deals, fliers should plan on purchasing tickets about two months in advance. In 2015, the best prices for economy tickets within North America were purchased 57 days in advance, which yielded 10 percent savings compared to the average fare.

The best news of all? 2016 is expected to be a great year for travelers looking to save money. Air ticket prices declined roughly 8 percent year-over-year between October 2014 and October 2015—according to the report, fare changes in a previous year can often be a good indicator of what's to come in the year ahead. A final tip? Purchase tickets alongside hotel and car rental reservations, which can save you nearly 20 percent on airfare.

Before you jet off, take a look at these 20 tips from air travel insiders. And make sure not to be one of these annoying passengers!