Frequent travelers are always trying to figure out the best day of the week to snag plane tickets, but here's the hard truth: The data is conflicting. Many travel experts claim Tuesday afternoons are the cheapest time to claim a flight, whereas data from the fare-predicting app Hopper claims Tuesdays aren't necessarily the best ticket-buying time.

The Argument for Tuesdays

Some experts argue that if you're looking to book a cheap flight, you should make the purchase on a Tuesday afternoon. Here's the argument.

On Mondays, airline officials check out how seats sold over the weekend and decide what the airfares should be based on that. On Tuesday mornings, they look at what competitors are charging for routes, and adjust their fares accordingly. By the afternoon, they've settled on the most competitive pricing, and that's why Tuesday afternoons are the cheapest time to buy a plane ticket. Prices usually rise again by Friday, so purchasing between Tuesday and Thursday is your best bet.

Still, demand ultimately determines airfares. The fewer seats an airline has left on a flight, the more expensive those available seats will be. So if you're trying to book a flight home for Christmas, for example, it's probably best not to wait around for Tuesday afternoon if you see a doable price, as such flights are usually in high demand.

The Argument for Other Weekdays

Hopper, an aviation insights company, has compiled airline data that conflicts with the usual Tuesday afternoon advice. Hopper has said Tuesday flights are usually cheaper only if you purchase them exactly at midnight, and even so, that saves only about $18 on average for 1.6 percent of domestic U.S. flights.

This data suggests that travelers book international flights on Thursdays. Out of 3,500 international routes, Hopper found that 900 offered their lowest booking prices (with an average savings of $20) on Thursdays. This beat out all other days of the week.

On Monday, Hopper found that 600 routes lowered their fares by an average of $30 a day, making Monday another particularly cheap day to purchase an international flight. Sundays had the worst deals for flight bookings.

Domestic flight fares, on the other hand, vary less in pricing as the week drags on. Hopper suggests to just book domestic flights as early as possible, especially with high-volume routes. But statistically speaking, Thursdays show the most common price drop for domestic flights, with the average savings ranging between $12 and $15. By contrast, Tuesday savings chalk up to an average of $10.