A brief introduction to key financial concepts is available at www.teachmefinance.com.

How much do you need at retirement? Check out the "Money/Retirement" link at www.about.com.

For a downloadable, Windows-based financial calculator, go to www.calculator.org.

Why does the Rule of 72 work? See www.datachimp.com.

Learn more about using Excel for time value and other calculations at www.studyfinance.com.