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. Related Content Dreaming Up an Active Retirement When you retire, how will you treat your next chapter? Acres of Diamonds In life it often happens that the answers to our most pressing questions are right in our own backyards. What Is My Life Expectancy? Estimate how many years you may need retirement assets or how long to provide income to a surviving spouse or children.