Randy Petersen, Mile Maven, answers your questions.

How can families get the most from their frequent-flier miles?

Some 10 trillion reward-program miles currently languish unused, and thanks to blackout dates limited seats and earlier expiration dates, it’s more difficult than ever to redeem them. But there are ways to work the system. Mileage pro Randy Petersen, creator of webflyer.com, which rates reward programs and ferrets out mileage-maximizing deals, fills us in.

Sign up the kids

When you pay for your child’s first fare, make him a member. I know five-year-olds with elite status.

Keep an eye on your account

Most miles expire after 18 months of inactivity. No plans to travel?Donate your stash to a nonprofit at miledonor.com.

Do the math

One mile on a round-trip domestic flight is worth about 1.2 cents. Multiply that by the distance you’re flying—then com-pare that figure to the lowest fare and decide whether you’re better off paying with cash or miles.

Be flexible

No reward seats available?Inquire about smaller airports nearby. Agents typically don’t mention them unless asked.

Know the network

Every carrier has “partners,” which means you can often hitch a ride on another airline.