Image: Airline © Blend Images, SuperStock

A few years ago, I started searching for the best ways to save money on airline flights. I wanted to see the world -- or at least the United States -- but I didn't have a bottomless budget. In the end, I found something surprising.

There is a group of people who fly for free by using a strategy that is the complete opposite of what most people do.

How to fly for free

It probably comes as no surprise to you that a great way to fly for cheap is by using frequent flyer miles. It's pretty simple: Cash in your miles, get a free flight and travel for less.

At first, I assumed that you had to fly all the time to earn frequent flyer miles. They are called "frequent flyer" miles after all. As it turns out, that's not true. The best way to earn frequent flyer miles isn't by flying at all. It's by finding the best credit card deals for earning frequent flyer miles, free hotel stays and rewards points.

Here's your bonus . . .

The credit card market is extremely competitive and very lucrative. As a result, credit card companies hand out huge frequent flyer bonuses to get people to sign up for their cards.

A typical bonus for getting a new credit card is 25,000 frequent flyer miles. Occasionally, you can get as many as 100,000 frequent flyer miles just by signing up for a new card.

In case you're wondering, 100,000 frequent flyer miles is enough to get you a round-trip business-class ticket from the U.S. to Europe. That's a value of about $5,000 for taking 10 minutes to fill out a credit card application.

Despite the huge payoff, I was still skeptical at first. How many cards could I apply for? Would this strategy hurt my credit score?

The 'churn'

As I read more about credit card bonuses, I stumbled upon a group of people called "churners."

Credit card churners are people who churn through credit card applications on a regular basis to get as many frequent flyer miles as possible. They apply for a card, spend the minimum amount necessary, get the frequent flyer miles, cancel the card a year later, and then do it all over again.

Some churners are so consistent with their efforts that they have earned more than a million frequent flyer miles in a single year. With that many miles, you could literally fly around the world multiple times for free.

Churners find out about credit card deals from a variety of websites, blogs and forums. There are even free email newsletters like CreditCardFlyers.com that will send you a brief update of the best credit card deals.

How to keep churning from hurting your credit

Credit card churning will not hurt your credit score if you do two things:

  1. Pay your balance in full every month.
  2. Carry little or no debt.

In fact, if you do those two things, churning may actually have a positive impact on your credit score. This is because you are getting more overall credit by applying for new cards, but you are spending about the same amount as before. This causes your credit-utilization ratio to drop, which can actually improve your credit score.

If you pay your balance in full and carry no debt, it is very unlikely that you will make a major credit card mistake, and you will see little or no impact from churning.

As a reminder, I want to be very clear about this: Credit card churning is not a good idea if you do not pay your balance in full every month. I advocate living a life with no debt, and I suggest you do whatever you can to lower or erase your debt.

But if done right, churning credit card bonuses and racking up frequent flyer miles is a great way to fly for free.

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