Vacancy rate is one of the most direct performance indicators available to property owners and managers. It tells you, at a glance, how much of your rentable inventory is sitting idle. The standard formula is straightforward: Vacancy Rate (%) = (Number of Vacant Units / Total Rentable Units) x 100. For a time-based view, you can also calculate it as: Vacancy Rate (%) = (Total Vacant Unit Days / Total Available Unit Days) x 100. The time-based version is more useful when units turn over at different points in the month, because it captures partial-period losses rather than giving you a simple snapshot at a single point in time.
Understanding vacancy rate matters because empty units are not neutral, they are actively costly. Every day a unit sits vacant you lose that day's rent while still carrying fixed expenses: mortgage, insurance, property taxes, and utilities. Beyond the lost rent, there are turnover costs tied to the vacancy itself, including cleaning, minor repairs, and marketing. Sophisticated investors track effective gross income (EGI) alongside vacancy rate because EGI already deducts vacancy loss from potential gross income, making the real revenue picture visible before expenses are subtracted. A property with a 10% vacancy rate and $120,000 in potential gross rent is only collecting around $108,000 in gross rent, and that $12,000 gap compounds across a multi-year hold.
Benchmarks vary by market and asset class, but most underwriters treat a 5% vacancy rate as a standard stabilized assumption for residential multifamily in healthy markets. Markets with tight supply often run at 2-3%, while Class C properties or oversupplied submarkets can see 10-15% or higher. The critical habit is comparing your rate to local comparable properties, not national averages. If your building is running 8% vacancy in a submarket where comparable properties average 4%, that gap points to a specific operational or pricing issue worth diagnosing: lease-up speed, rent pricing relative to market, maintenance responsiveness, or the quality of your marketing channels.
Worked example
A landlord owns a 20-unit apartment building. At the start of the month, 3 units are vacant. Using the snapshot formula: Vacancy Rate = (3 / 20) x 100 = 15%. This is well above the local market average of 5%, which flags an immediate problem. If each unit rents for $1,500 per month, those 3 empty units represent $4,500 in lost monthly rent. Over a 12-month period at that rate, the landlord would forfeit $54,000 in gross revenue. Reducing vacancy to the 5% market average (1 vacant unit) would recover roughly $36,000 per year, a meaningful improvement to net operating income without changing a single expense line.