Frequent flyer miles used to be simple. You flew on an airline, earned miles in its program, and used those miles for a free trip. But the game changed when banks started giving rewards on credit card purchases. Now, various credit cards offer three basic options:

• Co-branded cards award miles in the partner airline's program, typically offering one mile per dollar charged to the card, with occasional bonuses.
• Some cards operate their own travel programs, in which you can accumulate miles or points in your account until you want to travel, at which time the bank buys you a ticket. Those programs tend to give slightly higher point values for air tickets than for other cash purchases.
• Still others offer a straight cash payback, with the better cards giving 1.5 to 2 cents per dollar charged.

Road warriors generally know their best options, and their calculations include not only "free" trip awards but also elite status in airline frequent flyer programs, which provide bonus earnings, upgrades, and other benefits.

But travelers who take only a few leisure trips per year are not going to get upgrades or any other benefits that those really frequent flyers enjoy. Instead, they build their miles as they can and use them as they can. Their questions center mainly on whether to concentrate buying on a card that earns airline miles or one that returns cash or cash equivalent in travel buys.

Baseline Calculation: The Value of Airline Miles

Overall, most miles-and-points mavens seem to agree that airline frequent flyer credit is worth between 1 and 2 cents a mile. Among the domestic lines, most also tend to assign values hovering around 1.5 cents a mile. They typically assign above-average values to Alaska miles because of that line's favorable partnerships and below average values to Delta and Frontier miles.

But the value of a mile in any airline program depends in part on what sort of travel you buy with those miles. The most common use of miles is for a domestic coach round-trip ticket, and most programs give a domestic round-trip for 25,000 miles or so at the seat-restricted "saver" award level.

Last year, average airfares at three typical giant airports were $314 at O'Hare, $349 at Los Angeles, and $389 at JFK. Average fares at medium-size airports such as Spokane were generally about $100 more than at bigger fields, and statistics are not available for even smaller airports such as Bangor or Eugene.

In an airline program, if you could score a $400 round-trip for the usual 25,000 miles of credit, the value per mile is about 1.6 cents. But you have to adjust that figure down somewhat to reflect the difficulty of scoring saver-level awards. Moreover, Airfarewatchdog often shows transcontinental round-trips for under $200. Using 25,000 miles for that trip would drop the value to 0.8 cents.

Currently, July round-trips to Paris post at about $580 from Boston and $1,700 from Spokane. In economy, a transatlantic award on Delta goes for a minimum of 70,000 miles from Boston and 92,500 miles from Spokane. On United, the awards go for 60,000 miles in economy regardless of origin. So, for an economy round-trip to Paris, the value ranges from 0.8 to 1.5 cents a mile. But transatlantic tickets often go for much less, dropping the value of a mile substantially. In business class, the currently posted fares are $2,500 from Boston and $3,000 from Spokane. So in business class, the values range from 1.8 to 2.1 cents a mile.

Other things being equal, then, you can figure that a mile in any airline's program is worth somewhere around 1.5 cents when you use it for coach/economy air travel; more if you fly first or business class. Most airline programs allow you to use miles for purchases other than tickets, too, but those other purchases provide a value of only about 0.5 cents per mile and are therefore bad uses for the credit.

Credit-Card Points

Typical credit card programs award at least one point or mile per dollar purchased on the card. If you can transfer those miles/points to an airline account, they're worth the same as miles earned by flying.

But, these days, you have access to credit cards that award 1.5 to 2 points, worth 1 cent each, per dollar charged, which can often be more valuable than miles in any airline program. When you travel in coach/economy class, cash or cash equivalent is always better than airline miles: With cash, you can buy a ticket without the challenge of finding saver-level award seats, plus you earn more miles on the flight. The only time earning airlines miles on a credit card makes sense is when you plan to use those miles for business- or first-class travel.

The Take-Away: Four Rules to Live By

You could play around with dates and fares forever, but these sample calculations and others like it over the years lead to some general conclusions:

• Airline miles are worth about 1.5 cents each when used for coach/economy tickets; more when applied to premium-class tickets.
• Most travelers, other than road warriors, who use reward credit cards are better off by taking a cash payout of 1.5 up 2 cents per dollar charged than by using a card that earns airline miles.
• Airline miles can be worth more when you use them for high-fare trips—if you can get the award seats, and that's a big if.
• Buying airline miles, at a typical price somewhere between 3 and 4 cents per mile, is obviously a bad choice except possibly when you need a few miles for a specific award level.

 Editor's note: The opinions expressed here are the author's alone, not those of any bank, credit card issuer, airline, or hotel chain, and have not been reviewed, approved, or otherwise endorsed by any of these entities.