Here's the most recent web sound-bite about compounding. Again there are a lot of assumptions made in this example from the rate of return, to tax treatment (not as much an issue since it deals with a Roth IRA account), to being willing to ride out wild dips and swing:

http://moneycentral.msn.com/content/...ing/P73751.asp

Let's suppose that you are 16 years old, in high school, and willing to work. Let's also suppose that you can clear about $2,000 over the course of a summer, if only because a doting grandparent puts money in the Roth while you take your earnings to school. If you invest in a Roth IRA, it will grow, tax-free, for as long as you have the account. All withdrawals from the account after age 59 1/2 will be tax-free.

If your money is invested in common stocks and you achieve the average compound annual rate on large-capitalization U.S. stocks, 10.7%, your account will grow to $9,378 at the end of the fourth year. You will be 20 years old. Invested in the same way, with no additional savings, the account will grow to:

$25,917 by the time you are 30

$71,625 by the time you are 40

$197,943 by the time you are 50

$547,037 by the time you are 60

And $1,114,423 by the time you are 67