Avoid clipping your own wings

TO maximize your frequent-flier miles, there are several mileage pitfalls you must avoid:

Don’t waste your miles on cheap domestic tickets. Do the math. Most experts calculate the minimum value of one mile at 2 cents, or $20 per 1,000 miles. So the value of a 25,000-mile round-trip domestic coach ticket is $500. Don’t spend 25,000 miles on a round-trip coach ticket that you can buy for as little as $200.

Adopt a buyer-beware attitude about merchandise awards. Because of the mass of miles and the relative paucity of available seats, most programs let you redeem mileage for merchandise. Using the same formula, compare the value of your miles for a free ticket or upgrade with the price of the merchandise.

Use your mileage-earning credit cards carefully. Credit cards linked to the programs are a great way to rack up miles without flying. But credit cards in general are fraught with peril. Never spend money on something you don’t really need just to earn miles. Credit cards can also impose fees on certain transactions, such as tax payments. Before charging property or income taxes on a credit card, find out the fee and figure out if the miles earned are worth the cost.

Be equally cautious about your mileage program’s partners. Be a shrewd comparison shopper before you buy from affiliated retailers, sign up for telephone service or even refinance your home. Are you paying more money to earn the miles than if you took your business to a non-affiliated company? Or does the partner offer you a great opportunity to pick up some free miles for a fairly priced product or service that you were going to purchase anyway?

Don’t let your miles expire. Most programs clearly state that your mileage balance will expire if your account doesn’t have any activity in 36 months; that means any kind of transaction: a mileage withdrawal for an award, a mileage deposit from a program partner or a bonus for getting a credit card linked to that program, among others.

Regularly check the latest activity on all your mileage programs. Many fliers have one or two little-used accounts that are easy to forget about. Don’t let the miles expire, because when they’re gone, they’re gone.

A special caution to leisure travelers. “The harsh mileage-expiration policies of discounters such as Southwest and JetBlue mean that many less-than-frequent travelers have little chance of ever earning a free ticket,” says Tim Winship, publisher of www.frequentflier.com. JetBlue and Southwest miles expire after one and two years, respectively, even if there’s account activity.

Don’t sell your miles. That’s against most programs’ rules. The frequent-flier programs’ “mileage police” can scan websites such as EBay just as easily as you can. If the airlines catch you, they will cancel the free ticket and void the miles in the rule breaker’s account.