Luck often seems to be the most important factor in getting cheap airfares. How many times have you bought your tickets only to see “last minute” deals you could have gotten if you had been a little more patient?

Everyone has advice about the optimal time to buy tickets and the best days to fly. However, these suggestions are often confusing and contradictory. They leave you asking questions like “Am I supposed to buy my tickets on Tuesday or purchase them on Wednesday and fly on a Tuesday?”

Getting the absolute lowest fare every time you fly is impossible. At the same time, enough research has been done on price patterns that it is now possible to put the odds of scoring a cheap flight squarely in your favor. Think of it this way: Always getting low fares is not a realizable goal, but spending less — way less — over the course of your entire flying life is realistic if you understand how to play the odds.

Book now or wait?

After crunching the data from more than 4 million trips, the travel site Cheap Air found that the optimal time to get the lowest domestic fare was 54 days before takeoff. The ideal buying window is much larger than that single day, however. From 104 days until 30 days before departure, average prices were within $10 of the 54-day low.

This data proves that waiting for discounted fares to pop up a week or two before your travel date probably will not save you money in the long run. Even if an occasional deal is there, you will pay much more over time because you often will be stuck buying tickets at last-minute prices. Buying too early — more than 3 1/2 months before take-off — is also a common strategy that turns out to be less than ideal, according to the Cheap Air survey.

Of course, the 54-day rule is not universally true. For holiday travel, things are slightly different. The good news is that there is still a pretty large window for getting decent prices. Holiday fares were actually at their cheapest in June, but they stayed within a reasonable distance of this low point throughout the summer. The bad news: The good-deal window closes early. Prices for November and December flights start rising rapidly at the end of September. Also, because of the high demand for seats, last minute Thanksgiving deals are virtually nonexistent. Waiting until too late can literally cost you hundreds of dollars.

The best day to buy and fly

flight departures board

Flying on low-demand days is one of the best ways to save money. (Photo: Barta IV/flickr)

Recent data has also cast doubt on the conventional practice of buying tickets midweek. Statistics from Airlines Reporting Corp., a ticket processor for travel agents, showed that fares were cheaper on Sunday, on average, than fares on Tuesday. Increased reliance on the Internet to sell and advertise tickets is partially responsible for this switch. Tuesday does, however, have the highest percentage of sales (about 20 percent).

Conventional wisdom does prove true when it comes to choosing the best day to fly. The general rule is this: The less popular the day, the lower the fares. Tuesdays, Wednesdays and Saturdays are the least expensive options, on average. Traveling two or three days on either side of the most popular holiday travel days (Wednesday before Thanksgiving, for example) can lead to significantly lower fares — if you buy far enough in advance.

Deals for international travel

Though they pay much more than domestic travelers, international fliers have an easier shot at nailing down a good deal. Overseas fares fluctuate little between 10 months and three months before departure. This gives fliers a huge window in which to search for sales or dig up promotional codes. Another thing to keep in mind is that traditional brick-and-mortar travel agents have access to discounted fares from airfare consolidators (ticket wholesalers). They can often offer lower prices than third-party booking sites when it comes to international travel.

Different international destinations have different low-price “sweet spots.” According to Travel and Leisure, it is best to book Caribbean winter vacations five months in advance. Meanwhile, buying at least six months before taking off for a summertime vacation in Europe is usually the best policy.

Most people think that third-party booking sites offer the best deals. This is often the case, but not always. Some sales are listed only on an airline's website, and other “flash sales” are advertised to Twitter followers. Low-cost carriers rely on Twitter quite frequently, and JetBlue has a specific account it uses solely to announce special promotions.

For legacy carriers (American, Delta and United), the best policy is to get on a mailing list. These airlines will sometimes send coupon codes that offer discounts on certain fares. Of course, this strategy requires sifting through lots of promotional emails that will prove useless to you.

Southwest flight

Southwest Airlines offers free cancelation on standard-price tickets. (Photo: Kevin Dooley/flickr)

Don't forget refunds

Even after you have purchased a ticket, you can still find a better deal. Airlines are required by law to give you a full refund or to hold your ticket without charging you for 24 hours. Even if you have a nonrefundable ticket, they have to honor your request for cancelation. Of course, airlines and booking sites never advertise this rule to buyers.

Canceling outside of the 24-hour window can lead to significant fees (the average is $200 per ticket to change departure date). Southwest is the only U.S.-based airline that does not charge for changing a ticket. However, its promotional fares are often not covered under this policy.

Even with all this information, finding low fares can take a lot of legwork. But at least you will be able to maximize your chances of getting a good deal, or, at the very least, you can avoid paying more than you need to for a ticket.

When is the best time to buy airplane tickets?
Nothing can guarantee you'll always get a great deal, but here's how you can land lower prices more often.