6

Carrying a credit-card balance
Cost: $5,000 to $23,000

Owing money on a credit card is a costly mistake that can take its toll for a very long time. If you have a card with an interest rate of 15 percent and you pay only the minimum due each month, it will take you 22 years and 2 months to retire a $5,000 debt, and you'll have paid $5,729 in interest.

Some 45 percent of consumers maintain a credit-card balance that averages $2,200, according to the Federal Reserve. But Fair Isaac, the credit-scoring company, says 15 percent of consumers have balances of more than $10,000. We applied an average 15.2 percent interest rate to each of those balances and assumed the borrower got in the habit of carrying a balance for 20 years.

What you can do. Use credit cards for their convenience and for the basic protections they offer against fraud. But plan to pay off the balance in full every month to avoid interest.