Example

You are calculating a vacancy rate you can use in your various analyses. You have reliable information that a property had potential rental income last year of $673,229. The vacancy and credit loss was $41,393. What was the vacancy rate?

It's 6.1%. Round to 6%.

You use this rate for calculating the vacancy & credit loss.  A vacancy rate obtained from market research gives you a rate you can use in a forecast.

The Institute of Real Estate Management (IREM) makes the divisor gross possible income (potential rental income + other income rather than just potential rental income alone) for its statistical publications.