Want to Find a Cheap Flight? Do This One Thing

— -- Let’s get right to it: The one single thing you can do to find a cheap flight is to compare airfares. Always.

Sounds simple but it is important to demonstrate this because it is so very easy to unthinkingly pay too much for plane tickets. And there’s an art to comparing fares as you’ll see in the demonstration below.

When it comes to airfare -- or anything else for that matter -- why pay a penny more than you have to?

1. Always compare fares

You want to fly so you go online to shop. What you don’t want to do is only go to your favorite airline’s site or you risk paying too much.

The reason: No single airline always has the best deal.

Here’s just one example found on Nov. 11 for the same day of travel in December; the fares are round-trip prices (and may have changed by the time you read this):

New York to Los Angeles:
- Spirit: $404
- Frontier: $283

Perhaps you’re saying to yourself, "It figures that another discounter beat the Spirit price." Yes, but American also beat Spirit’s price, and so did Delta, and so did JetBlue, United and Virgin America. Yes, Spirit often has the best price, but not this time.

Tip: Always use an airfare comparison site and there are many including my own, but also compare prices at Southwest.com.

Southwest is the only major U.S. carrier that does not share its prices. Sometimes those prices are very good, so you won’t want to miss them.

2. Never make assumptions

Do not assume the "cheap airline" always has the best price; often it will but sometimes it won’t and if you don’t compare you may be paying a whole lot more. Example: If you travel as a family of four on the NY-LA itinerary above and buy from Spirit without learning about that cheaper Frontier price, you are shelling out an additional $484 on plane tickets that you didn’t have to.

Flagship assumption: Do not assume a country’s flagship airline will have a cheaper deal than another carrier. Here’s a good example using round-trip fares for flights to France in December found on Nov. 10.

New York to Paris:
- Norwegian Air Shuttle: $505
- Air Canada: $520
- United: $521
- Air France: $688

Notice that in this cases, the discounter (Norwegian Air) beat larger airlines, albeit only by a whisker, yet it romped past flagship carrier Air France.

3. Once you compare fares, make a thoughtful decision

Thoughtful decision on fees: Not everything comes down to dollars and cents of course; there can be hidden fees to consider. Let’s look at another round-trip fare for travel in December.

Los Angeles to Dallas
- Spirit: $77
- Southwest: $142

Wow, Spirit wins this contest handily, unless you factor in luggage. Southwest allows passengers a carry-on plus two checked bags for free while Spirit offers no free bags (actually, Spirit does allow a very small bag for free, but only if it fits under a seat and stays there). If you want to travel with a single normal-size carry-on bag on Spirit, it will cost $35 one-way or $70 round-trip which raises the total price of the Spirit flight to $147. In this scenario, the $142 Southwest fare is cheaper.

Thoughtful decision on convenience: Sometimes the cheapest deals are connecting flights (and this is a simple way to save on many flights, sometimes as much as 50 percent). But do you have time for this inconvenience? Or are you traveling with little ones who may not be able to endure a longer travel day? Only you can factor this into your fare, and come to a final decision on the best price for you.

Rick Seaney is the CEO of FareCompare, a website that curates the best deals on flights from around the world. Any opinions expressed in this column are solely those of the author.