A handy little calculation for the duplex investor is the rule of 72s. The rule of 72s calculates the amount of years it will take to double the value on an investment duplex at a certain appreciation rate.
To do this, you simply need to plug-in the appreciate rate rounded to the nearest whole number into 72 and that will tell you how many years it will take a duplex property to double in value.
You purchase a duplex for $150k and has an appreciation rate of 9%.
72 / 9% appreciation rate = 8 Years
It would take a $150k duplex 8 years at a 9% appreciation rate for that investment duplex to be valued at $300k.
This is a quick and handy way to see how the appreciation rate relates to your investment duplex.