How do you determine vacancy rates

[Vince Greenland]

This is obviously a very important measure of success of a multi-family complex. However, we have approximately 90 units and are looking to expand, so the calculation becomes a little tricky.

i am looking for some ideas how others quickly determine vacancy rates at the end of the year. in the past i have taken our current rent roll (assuming 100% full) and compare to the annual income. i know it has some holes due to rent increases during the year that may skew the numbers.

So, if someone asks you what is your vacancy rate, how do you answer the question? if you say a %, how are you calculating it.

thanks