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 What Can a Million Dollars Buy You? $1 million in a diversified portfolio could help finance part of your retirement. The Business Cycle Understanding the economy's cycles can help put current business conditions in better perspective. Taxable vs. Tax-Deferred Savings Use this calculator to compare the future value of investments with different tax consequences.