There are dozens of Web sites that provide calculators to help with personal financial decisions. Two good examples are www.quicken.com and www.smartmoney.com (Note that both calculators assume simple interest to convert the monthly interest rate to an annual rate. In other words, the annual interest rate is quoted as 12 times the monthly rate.)

1. Suppose you have $5,000 in the bank and plan to save $500 a month. If you earn a return of 12% a year (1% a month), how much will you have accumulated by the time you retire in 30 years? Now log in to the Quicken site and click on Bills and Banking to find a nice savings calculator. Use this to check your answer.
2. Suppose you take out a 30-year mortgage loan of $200,000 at an interest rate of 10%. What is your total monthly payment? How much of the first month's payment goes to reduce the size of the loan? How much of the payment after two years goes to reduce the amount of the loan? You can check your answers by logging in to the personal finance page of www.smartmoney.com and using the mortgage calculator.