The Rule of 72: What Makes it Tick?

And when does it fail?

Image by P. Venkat Raman

The Rule of 72 is a guideline to estimate how long an investment that earns compound interest takes to double. This guideline helps you plan your investment mix in several ways. Much has been written on this topic, right here in Making of a Millionaire, and elsewhere on Medium. And, of course, on the web.