The Rule of 72 is useful for understanding compound interest because it shows the approximate time or interest rate required to double a sum of money (e.g., $2,500 to $5,000).
To apply the Rule of 72 to your own personal investments, you need to know or assume their expected rate of return. For example, you may own a bond that you know will regularly pay 6% interest until maturity or assume that the average annual return on your stocks is …