It can be hard to book a flight at the last moment.

Almost all of the seats are full and everything is more expensive. You have to refresh all the airlines websites or conduct a search after searching for something on the internet. It can be hard to find something at the last minute.

It doesn't have to be hard to find a good deal on a plane. If you book at the last minute, we have rounded up some tips from expert flyers so you don't have to pay high fares.

Why do fares get more expensive the longer you wait?

You would think that everything would be cheaper as airlines try to sell more seats, but that is not the case. It's the other way around. Airfare increases at the last moment. It is important to know why flights are more expensive the longer you wait to book.

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Chuck Thackston is the managing director of data science at Airlines Reporting Corporation.

Thackston said that airlines usually put flights on their schedule and set a fare for that flight way out. They don't do a lot of changes until it gets closer to departure.

Business travelers often book at the last minute and airlines can often charge the highest fares.

In the past, fares used to be cheaper at the last minute as airlines used to lose revenue if they didn't fill seats. Scott Keyes, the founder of Scott's Cheap Flights, said that the people who were buying last-minute seats were business travelers.

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Business travelers are willing to spend a lot of money on airfare because they don't have to pay taxes. Those expensive fares on airlines websites start a couple of weeks before your travel date to target business travelers, not leisure travelers.

Keyes said that airlines realized that they were in the business of killing seats. We are in the business of making as much money as possible. The price on last-minute flights won't make the most money. It's to increase the price on flights at the last minute.

When’s the sweet spot to book my tickets?

The best time to book your flights is between one to four months in advance for domestic flights and six months for international flights, according to travel experts we spoke to.

That is confirmed by the data. The average fare in the 120 to 30 days before you travel is the same. You could save up to 10% on airfare if you booked international travel at least six months in advance.

According to an economist at Hopper, prices are at their lowest one to two months before, as people may be searching for flight tickets but not actually booking. Airlines can charge more for the remaining seats if the flights start to fill. Those who don't have a lot of flexibility with their travel dates will have to book the most expensive fare.

Berg said that lower prices are usually due to not many people booking yet.

The window for booking domestic flights is one to three months. Two to eight months in advance is the "Goldilocks window" for international flights.

If you want to book flights for Christmas or Thanksgiving, you have to book them before the holiday. The rule is to book those flights by Thanksgiving, but it is always better to book them as soon as possible.

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The earliest bird doesn't always get the worm. If you book your flights a year in advance, you will pay more for them.

Most airlines begin selling airfare about 11 months before travel. When airlines begin to put tickets up 11 months out is not a good deal.

How much does timing matter?

An Alaska Airlines plane takes off from Seattle in November 2022. CLINT HENDERSON/THE POINTS GUY

Booking flights is dependent on timing.

The specific day when you book your flight has the most influence on airfare. Berg said flights that leave on a Tuesday or a Wednesday are a good spot for a deal.

Thackston said that average fare prices for leisure travel tend to be lower on the weekends due to more leisure travel tickets being purchased.

Fare increases can be caused by the popularity of a destination during a specific time of year. It can be hard to find a good last-minute deal if you visit New Orleans in February or New York City in December.

Thackston said it's as simple as supply and demand. If you want to fly to a popular destination during a popular time, those flights tend to fill up and you won't get as good of a deal as it approaches departure day

You are more likely to find a good deal last minute if you book your flights in the middle of January or before Christmas.

A cheap, last-minute Christmas flight is an oxymoron. It is very rare. The two least popular months of the year for travel are January and February.

Is the destination important?

It is dependent on the situation.

Competition is a factor that determines airfare prices. As airlines are vying for as many customers as possible, a popular route such as New York City to Miami may be less expensive. It might be more expensive to travel from Ohio to New York City.

You would be more likely to find a last-minute deal from New York City to Miami than from AK to New York City. Domestic flight deals are more likely to be found than international ones.

Berg said it can be difficult to find a last-minute deal for leisure destinations because the passengers who booked those tickets most likely did so in advance. As more people are interested in booking, airlines are more likely to raise their prices.

If you want to avoid overpaying for tickets to leisure destinations at the last minute, you should fly with a budget airline. Budget airlines don't have the same power to raise fares like Delta Air Lines or American Airlines do.

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Business travelers tend to pay more for last-minute flights because airlines are trying to make more money. Budget airlines tend to have mostly leisure travel clientele. They don't have the same power to raise last-minute fares like United, American and Delta do.

What about 'hidden-city' booking?

Travelers booking a flight with a stop in the city they want to visit is called a "hidden-city" booking. The passengers don't board the next segment once they reach the layover city.

It's possible to find a better deal on a flight from Newark to Austin with a stop in Charlotte. All you have to do is leave the plane and not board the next flight from Charlotte to Austin.

The hidden city method is not recommended by the experts because it comes with a lot of uncertainties.

Since checked baggage goes to the destination printed on your ticket, you can only bring a carry-on.

Round-trip tickets will be canceled if you miss a segment on the flight. If the layover destination changes from Charlotte to Washington, D.C., you can't say why you need to be in Charlotte.

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An airline could ask you to pay more for your flight or even ban you if you use this tactic too frequently.

Berg and Thackston suggested booking flights with a travel agency instead of using hidden-city booking.

Thackston said that shopping for airfares can be difficult if you aren't used to it. If you want to find the best deals, you can use a professional travel agent or an online travel agent.

Can you find a last-minute deal using miles and rewards?

It is not easy.

It is more difficult to find a bargain in miles at the last minute because they are closely correlated with cash prices.

Keyes said that the opportunities for value are more limited now.

It is worthwhile to check to see if there is anything in the awards space. Last-minute flights to Hawaii in miles are offered by United and Delta. You have to act quickly on mileage deals as they are more likely to change frequently.

Berg said that if you have a credit card with a mileage program, you can potentially book a basic economy ticket and have your bags checked in for free.

Berg said that it's important to think about the total cost of your trip because you might get a great deal on airfare but end up paying a lot of fees. You can get a bag or two free depending on the airline, if you have a credit card.

Other tips for booking last-minute fares

If you have to book a flight at the last minute, all the experts we spoke to gave you a number of tips.

The longer you wait, the more likely the fares will rise. The timing of your booking is also important. Travelers who book on Sundays are more likely to save on domestic and international flights.

Travelers can save up to 15% on airfare if they leave on Wednesdays. It's the most expensive to leave from Saturday to Monday.

The latest you can book your flight is at least 21 days in advance, according to Keyes.

The fare is only available up to 21 days before the trip. The fare ends on day 20. The cheapest flight is going to be more expensive because it is no longer available for purchase.

Berg said that it's important to be flexible for last-minute flights.

She said that if you want to get a good deal, be flexible. Good deals can be unlocked by that.

Bottom line

It can be difficult to find a last-minute deal.

It is always a good idea to book your flights when you see a good deal.

It's possible to find good deals days before departure, but you'll often find yourself choosing a less desirable destination. Even for the more experienced traveler, hidden-city booking can have too many problems.

If you want to find deals on airfare, try to book them at least 21 days before your departure date and be flexible. You don't have to pay more for flights. The chances of finding a cheap flight are slim.