I'm probably leaving out key information, but using a compound interest calculator at this site --
http://www.moneychimp.com/calculator...calculator.htm -- I entered the following values:
Principal: $1,500
Years to grow: 40
Interest is compounded four times annually (quarterly)
Interest rate: 12 percent (which I thought was generous over the course of 40 years; some years the market will do better, other years worse)
The calculated future value comes to $169,842.
Changing the interest rate to 15 percent results in a future value of $542,235.
EDITED TO ADD: I was typing as Max was posting. I think we're making the same point.