If you’ve never heard of the 24-hour rule, I suppose you’re forgiven. Browsing through the Federal Register isn’t your idea of a good time? But if you know just one Department of Transportation regulation, make it the 24-hour rule. It’s saved me thousands of dollars in airfare, and it can for you too.

If you’ve never heard of the 24-hour rule, I suppose you’re forgiven. Browsing through the Federal Register isn’t your idea of a good time? But if you know just one Department of Transportation regulation, make it the 24-hour rule. It’s saved me thousands of dollars in airfare, and it can for you too.  What is the 24-hour rule? The 24-hour rule is a federal regulation that automatically entitles you to a 24-hour grace period from the moment you purchase a flight during which you can cancel and get a full cash refund. It covers all flights to or from a US airport, even on a foreign airline, so long as: The flight is at least 7 days away It was booked directly with the airline, rather than an online travel agency (For pedants, the rule technically allows airlines to choose between offering a 24-hour hold or a 24-hour refund window, but en masse U.S. airlines have opted to offer the latter.) In addition to giving you clemency for any regrettable drunken flight bookings (not me I would never), the 24-hour rule can be especially helpful in two scenarios.  Scenario 1: Mistake Fares Let’s say we all get lucky and tomorrow morning a Mistake Fare—$169 roundtrip to Paris—pops up. You go to call your partner and coordinate the best date, but then you remember they’re in a meeting all day. Shoot! You could wait until they get home, but fares this good don’t tend to last long. Six hours if we’re lucky. Instead, the 24-hour rule comes in handy. Rather than risk the deal disappearing, you take your best guess about which week works best for their schedule and book it. If it turns out they’re busy that week, the 24-hour rule lets you cancel for a full cash refund. Plus if you want to be really extra, you could book two or three different weeks—one in April, one in May, one in June—and keep the one (or more?) that works best.  Scenario 2: Fare wars Every so often, airlines will get in fare wars, undercutting one another on certain routes tit-for-tat. These skirmishes can sometimes go on for days, and cheap flight lovers are always the real winners. Let’s walk through an example. Say you live in Atlanta and you’ve been really hoping to visit Barcelona. You get an email one morning that Delta flights from Charlotte to Barcelona are on sale for $380 roundtrip. Score! A fare like that is worth the four-hour drive to Charlotte, so you pull the trigger. Not three hours later, you get another email: American has responded by offering flights from Atlanta to Barcelona (with one stop) for $350 roundtrip. Even better! With the 24-hour rule protecting you, you swap out for the Atlanta-departing flight, save yourself the drive, and pocket the $30 difference. But then that evening, Delta ups the battle by offering nonstop flights to Barcelona for the same $350 price. Direct! You take advantage of the 24-hour rule again and wind up with the best of all worlds, a cheap nonstop flight from Atlanta to Barcelona.  Be sure to book your new flight before canceling your old one Let’s say Trae Young snagged that one-stop Atlanta-Barcelona flight on American. Even NBA superstars know a great deal when they see one. Hours after booking, though, he got an alert about the nonstop Delta flight. Young, a cheap flight aficionado, knows that the 24-hour rule lets him cancel the original booking and take advantage of the new fare. But right after he cancels his American flight, the nonstop Delta fare disappears. (This is a prime example of the Hotcakes Principle: the better a fare, the shorter it tends to last.) He tries to reinstate the American flight, only to be told that once you cancel, there are no takebacks. In the end, Young is left with zero cheap Barcelona flights. One simple trick could have prevented this: booking the Delta flight before canceling the American one. That way, if the Delta deal disappears as he goes to book, he’d still have the original American flight.  OTA’s 24-hour cancellation rules The 24-hour rule federal rule only applies when you book directly with an airline, but a handful of major OTAs like Orbitz and Priceline offer their own 24-hour cancellation policies as well. With some OTAs, if the 24-hour window falls on a weekend or holiday, you may get an even longer refund period. While these OTA offerings can be useful and are generally reliable, it’s important to recognize that they lack the same legal protection as the federal 24-hour rule. And if an OTA doesn’t have a self-service cancellation option (as virtually all US airlines do), then a long customer service hold could push you outside the 24-hour refund window by the time an agent picks up. Love, Scott