A great general rule to govern compound interest rates is the rule of 72. Basically it answers the question, “How long will it take for me to double my money?”. Conversely, it can also answer “How much annual returns must I gain in a given time if I want to double my money?”. To best explain this concept, let’s look to an example. Let’s say I invest in a certain stock (AAPL) and I expect annual gains to average 10% in the next twenty years. I then divide 72/10 and get 7.2. This means it’ll take me approximately 7.2 years to double my money when it’s growing at a rate of 10%.