Not only will you likely pay more if you book a flight at the last minute, but purchasing tickets too early also can cost you. iStockphoto By Cameron Huddleston, Former Online Editor February 18, 2015 Get the timing right on your purchase of airline tickets and you can save a lot of money – $319 per ticket, to be precise, according to a new study by CheapAir.com. That’s the average savings the airfare shopping engine found travelers could achieve by buying the day when fares for a domestic trip were lowest versus the day when they were highest.SEE ALSO: 6 Costly Airline Fees and How to Avoid Them So when is the optimal time to buy a ticket to get the lowest price? CheapAir monitored fares for about 5 million flights in 2014 over a booking period ranging from 320 days in advance to one day in advance. Its researchers found that fares for domestic flights were lowest 47 days in advance. That’s an average, though. There’s actually a prime booking window between 114 days and 27 days before departure when fares for U.S. flights are the best. “Way more often than not, the best fare for a domestic trip will be offered at some point during that window,” says CheapAir CEO Jeff Klee. Fares shoot up an average of $111 if you wait to buy a ticket 14 days in advance of a flight and jump an average of $174 if you buy a ticket within seven days of departure. But you can also pay more by booking too early – an average of $50 more per ticket if you buy when flights first open for sale, according to the CheapAir study. Advertisement Of course, there are exceptions. Although there is a prime booking window when fares typically are lowest, the best time to buy airline tickets can vary greatly depending on destination, time of the year and travel days. In certain cases, it’s better to purchase tickets before the prime booking window. Here are some guidelines: Book early for summer, holiday and family travel. CheapAir recommends booking flights for summer travel to popular destinations and flights around Thanksgiving and Christmas much earlier than 47 days in advance. It also pays to book earlier when traveling with four or more people who want to sit together on a flight. Begin checking fares once a week as soon as you know when and where you are traveling to get a sense of the market, Klee says. If you see a good price, don’t wait for it to go lower because it’s more likely to rise than drop. To help monitor ticket prices, you can sign up to receive fare alerts from Airfarewatchdog, CheapAir or Kayak. Book very early for international travel. Fares for international flights don’t drop much from the time they open for sale 335 days before departure, according to CheapAir. About 90 days before departure, fares start climbing dramatically. For flights to Europe, it’s best to book at least 276 days in advance to get the best price. The best time to buy tickets to the Caribbean is 144 days in advance, on average; 318 days in advance for flights to Asia; 262 days for flights to Africa; 251 days for Mexico; 244 days for the South Pacific; 213 days for the Middle East; and 96 days for Central and South America. More ways to save Be flexible. The CheapAir study looked at lowest possible fares without regard to airline, flight time or number of stops. You’ll usually save the most money by booking flights with connections, or flights that are early in the morning or late at night. Also, flights on Tuesdays, Wednesdays and Saturdays tend to be cheaper, according to FareCompare.com. You can use a flexible search option on travel booking sites, such as the ones at Bing Travel or Kayak, to see which days have the best fares. Otherwise, you need to book early to get the best price on a nonstop flight that leaves at a desirable hour. Advertisement Watch your fare after your buy. Many airlines and online travel agencies will give you a rebate (usually in travel credits or vouchers) if your flight’s price drops below what you paid. You can sign up on Yapta.com to receive alerts if the price falls on a flight you've booked. Be aware, though, that some airlines can charge hefty fees for re-booking a flight to get a lower fare. It's not worth it to make a change if the fee outweighs your rebate. However, if you book a ticket through CheapAir, you can get a credit of up to $100 per passenger for future travel if the price of your ticket drops. You don’t have to re-book your flight (and possibly incur fees) to take advantage of the site’s Price Drop Payback credit.