Don't wait any longer to book your summer travel, says Scott's Cheap Flights founder

If you're planning on taking a vacation this summer but haven't booked your airfare yet, it's time to stop waiting.

That's because plane ticket prices for the peak summer travel season are only likely to go up from here, according to Scott Keyes, founder and CEO of Scott's Cheap Flights, a Portland, Ore.-based newsletter that sends daily airfare deals to 2 million-plus subscribers. 

"You want to make sure you don't put it off until the very last minute in the hopes that fares are gonna get cheaper because in all likelihood, the opposite is going to happen," he tells CNBC Make It.

While there is a common belief that holding out until closer to the travel date might allow you to score a last-minute deal, Keyes said this strategy is more than likely to blow up in your face and leave you with a more expensive ticket than if you had booked earlier.

"It's important to bear in mind that last-minute flights are not equally expensive," Keyes says. "A flight booked one month before travel is almost certainly going to be cheaper than a flight booked one week before travel, and a flight booked one week before travel is almost certainly going to be cheaper than a flight booked one day before travel."

At this point in the year, Keyes advises prospective travelers who are looking to fly between late June and early August to book the best price they can find now. Otherwise, he says, good deals likely won't be showing up again until after Labor Day.

When it comes to finding a good deal, Keyes says there's no need to compare prices between platforms like Expedia, Orbitz, Google Flights and Skyscanner, because they're "basically going to show you the same flights."

Instead, Keyes says the most important thing to do is to book directly through the airline. When you do this, you'll be protected by U.S. Department of Transportation regulations that require the airline to give you a full refund within 24 hours of booking.

"This 24-hour rule can both give you time to decide if you actually want to take this trip and it can also give you a sort of grace period to be able to take advantage of any future price drops, whether it's on your airline or a competitor airline," he says.

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