Six million Americans have already booked their holiday flights — but while they may have chosen from the most options when booking (and dodged the stress of having to worry about it later), they likely spent more than they would have had they waited until mid-fall.

"The early birds probably didn't get the best deal," said Robin Saks Frankel, an analyst at Bankrate.com, referencing research from Hopper. “The best time to book for Christmas is early October, while flights for Thanksgiving remain stable through the end of October."

Not what you expected? You’re not alone. The idea that the earlier you book, the more you’ll save is a common one.

Why it’s cheaper right now

Even Bankrate’s Saks Frankel was surprised to learn that buying in summer or even early fall doesn’t net you the best prices on airfare. But this is actually becoming something of a trend.

“We also saw [this] last year,” said Kimberly Palmer, personal finance expert at NerdWallet. “October seems to be the sweet spot for holiday travel deals, with prices fluctuating based on the supply and demand of flights.”

Zach Honig, editor-in-chief at The Points Guy, explained that airfares “drop considerably,” after the end of summer. Furthermore, “airfares are based on demand, so demand is likely lower during the October time period, as leisure travelers reserve vacation days for holiday periods when they can make the most of a long trip.”

"Once November starts, ticket prices are going to go up, and will continue to soar."

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Bear in mind that you don’t want to wait past that October “sweet spot,” as it were. Once November starts, ticket prices are going to go up, and will continue to soar on through the remainder of the season.

“Prices go up once you are within three weeks of the departure date, and even more so once you are within 10 days, so you could definitely end up paying more if you wait until the last minute,” said Palmer.

And of course, it should be noted that for many people, it’s not realistic to wait until October to finalize holiday plans.

"Most people are working with a limited amount of vacation days and can't run the risk of specific flights or accommodations selling out, so any additional expense incurred by advance booking is worth it for peace of mind,” said Corinne McDermott, founder of HaveBabyWillTravel.com.

Get a bonus from your credit card

Bankrate’s survey revealed that 33 percent of travelers book their flights directly through an airline’s website, while 25 percent use a travel comparison site. Just five percent use their credit card’s website (aka, shopping portal) to book their travel.

Yet using your credit card’s website to book your airfare is an easy way to rack up points or other rewards such as cash back. Every rewards credit card is different, but the gist is the same for pretty much all of them: Use the portal (and the designated credit card) to pay for goodies, and the more you spend, the more you’ll get in return. It’s designed to be a win-win for everyone: the credit card company, the airline (or other vendor), and you.

“I am surprised at how few people are going through their credit cards’ websites to book the flights to make sure they are getting the most out of their rewards,” said Palmer. “That indicates a lot of people are probably missing out on travel savings.”

Um, so how do we do that?

Why are so few people taking advantage of these cushy rewards? For starters, they may not know these credit card portals exist.

“You have to kind of look for these portals, and [learning how to navigate them] requires some patience,” said Bankrate’s Saks Frankel, adding that though more and more credit card companies are providing them, it takes some poking around.

It may take time, but the payoff is clear, and if you don’t have a credit card that offers bonuses, you may want to consider signing up for one now — they heap on the rewards incentives for new customers.

“Many of these travel rewards cards that charge an annual fee might waive it the first year,” said Saks Frankel, who recommends putting big expenses on the credit card (so long as you can promptly pay it off) in order to activate the rewards immediately.