The Rule of 72 Do you know how long it may take for your investments to double in value? The Rule of 72 is a quick way to figure it out. Share | Related Content From Boats to Brokers From the Dutch East India Company to Wall Street, the stock market has a long and storied history. What’s Your Investment IQ? You make decisions for your portfolio, but how much do you really know about the products you buy? Try this quiz Saving for College This calculator can help you estimate how much you should be saving for college.