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 Should You Invest in Exchange Traded Funds? There are hundreds of ETFs available. Should you invest in them? How Stocks Work Understanding how a stock works is key to understanding your investments. Keys to Investing for Retirement There are some key concepts to understand when investing for retirement.