If it’s 21 days before you plan to travel and you haven’t seen a flight deal to your destination, go ahead and book, Keyes advises. That’s because airlines’ automated fare systems are configured to treat later bookings as last-minute business traveler flights and price them accordingly (high, in other words). “The 21-Day Rule is still the gold standard if there’s a flight you’re looking at and it’s getting close and you’re trying to decide whether to book or not,” Keyes says.

Case in point: For a family holiday trip, Keyes had been monitoring airfare from Portland to Las Vegas, which had been stable for weeks at $113 per person. Then, Keyes noticed it increased by $99 twenty days before the trip, and again after the 14-day mark, it spiked another $89 (he purchased it before those increases, by the way). “Airfare is incredibly volatile—it goes up, it goes down, seemingly at random—which is why the 21-Day Rule is so important: it’s one of the few times you can know with virtual certainty that airfare is going to get more expensive,” he explains.

In addition, Keyes adds that the 21-day rule helped inspire the new “My Trips” feature in Going’s app “to help travelers monitor prices for their specific trips and receive real-time booking guidance.”

If you haven’t yet firmed up your summer vacation plans for 2025, it’s time to get moving—especially if you have your eyes set on a trip to Europe. According to Google Flights, the best time to book flights from the US to Europe is at least 72 days prior to departure. And flights to Europe tend to increase over time, especially at about 10 weeks prior to departure.

Try a last-minute rewards search

Last-minute flights can be a smart time to burn off frequent flier miles, as airlines will sometimes release unsold seats as cheaper-than-normal mileage tickets. Don’t just search online for these, though; sometimes, it may be worth calling the airline’s customer service number or chatting online with a rep, even if the rewards app or website shows no redemption opportunities.

This is also a good time to make sure you’re using the right credit card for your travel habits and airline loyalty, which can easily pay for flights through points. There’s a learning curve involved, but it’s never a bad time to get started, especially since most major credit cards offer significant sign-up bonuses several times a year. All major airlines have their own credit card (or one that’s co-branded with a bank), and most major banks, including Chase, CitiBank, and Bank of America, also offer travel-specific cards that can offer big-time savings on flights (plus hotels and more travel expenses).

Consider fifth freedom flights

Fifth freedom flights, in which an airline offers service between two countries outside of its home base, can be a boon to budget-minded travelers for several reasons. First of all, they’re often serviced by larger aircraft on popular international routes, which means more competition and lower prices, and they also sometimes offer overlooked frequent-flier availability—all of which can translate into significant savings, not to mention a superior onboard experience.

Try “hidden-city” booking (but be aware of the risks)

Say you need to fly from Boston to Phoenix, but the price is out of your budget. You could instead try to book a so-called hidden-city ticket: a flight with a layover where the passenger simply stops flying at the connecting city. (So you would book a flight from Boston to Los Angeles via Phoenix, and deplane in Phoenix with no intention of traveling on LA-bound leg.) Booking a longer flight with a layover can be significantly cheaper than a direct flight.