Here is a great little parlor trick to calculate the approximate number of years for an investment to double in value at a particular rate of compound interest.
Simply take the rate of growth and divide it as a whole number into 72. Keep in mind that the answer is not precise; you would need to divide into 72.73 to nail the exact amount.
Number of Years to Double in Value (approximate) = 72 / Rate of Growth
You purchase a piece of property for $100,000 in an area where property values have grown at 8% annually. If they continue to grow at that rate, about how long will it take for the property to double in value?
Number of Years to Double in Value (approximate) = 72 / ...