Vacancy rate is the ratio of the number of current occupied units compared with the total of units in a development, usually expressed as a percentage. If the calculations are done on a single property, vacancy rate can also be understood as a percentage of the time the property will be vacant per year, while trying to be rented out. Usually this amount has to be estimated for the calculations and depends mainly on the current rental market and the type of property. Often the vacancy rate can be estimated between 3 – 15%. Zero vacancy rate is not probable and if it occurs in reality, most probably the units are rented for less than a current market rent.