Using frequent flyer miles for a free flight or an upgrade is a nice perk, but you want to maximize the value of your miles. Sometimes it's better to actually pay for a flight instead of redeeming your miles.
There is no set value for frequent flyer miles, but it is generally accepted the value of each mile is somewhere between one and two cents.
If you're traveling first class, compare the cost of a first-class ticket vs. buying a coach ticket and using miles to get a free upgrade.
If your flight is not expensive, save your miles. For instance, if you cash in 25,000 miles to get a free ticket that's selling for $250, you're only getting one penny per mile. Use miles for more expensive flights.
Expired miles are worthless, so if yours are about to reach their expiration date, use them for whatever you can.
Some airlines offer a "cash and miles" option to purchase a ticket at a reduced rate provided you redeem a certain amount of miles. For instance, you might get a flight for 10,000 miles and $150.
