What Vacancy Loss Actually Means in Multifamily Underwriting
Vacancy loss is the rental income a property cannot collect because one or more units are unoccupied. It is not a soft estimate or a buffer you add at the end of your spreadsheet. It is a real subtraction from Gross Scheduled Income (GSI) that flows directly into your Effective Gross Income (EGI) and, from there, into your NOI.
Here is how the income waterfall works:
- Gross Scheduled Income (GSI): Total rent if every unit were occupied at current market rates, twelve months a year.
- Less Vacancy and Credit Loss: The income you will not collect because units sit empty or because tenants do not pay.
- Equals Effective Gross Income (EGI): What the property actually produces before expenses.
- Less Operating Expenses: Taxes, insurance, management fees, maintenance, utilities, and similar costs. Mortgage payments and capital expenditures are excluded from this line.
- Equals Net Operating Income (NOI): The number that drives valuation, cap rate analysis, and debt service coverage ratios.
Credit loss is often bundled with vacancy loss in underwriting. It captures income lost from non-paying tenants rather than empty units. For small multifamily properties in NC, a combined vacancy and credit loss factor of five to eight percent is a reasonable starting assumption for stabilized assets in strong rental corridors, though you should always verify against local data before finalizing your model.
When you are reviewing a seller's rent roll, pay close attention to how they present income. A common red flag is a pro forma that shows GSI with no vacancy deduction at all. The NC multifamily rent roll red flags that kill deals article covers what to look for before you trust any income figure a seller hands you.
The Step-by-Step Vacancy Loss Formula (With a Triplex Example)
The core formula is straightforward:
Vacancy Loss = Gross Scheduled Income (GSI) x Vacancy Rate
Working through a concrete example makes it easier to see how each step connects.
Suppose you are evaluating a triplex in Durham. Unit A rents for $1,100 per month, Unit B for $1,200, and Unit C for $1,050. The GSI is $3,350 per month, or $40,200 annually.
Step 1: Determine GSI. Add all unit rents at full occupancy. In this case, $3,350 per month.
Step 2: Establish your vacancy rate assumption. You are not using the current occupancy the seller reports. You are using a market-supported rate based on comparable properties and local conditions. For a stabilized triplex in Durham's rental market, a seven percent vacancy rate is a defensible starting point. We will use that figure here.
Step 3: Calculate vacancy loss. Multiply GSI by the vacancy rate. $40,200 x 0.07 equals $2,814 in annual vacancy loss.
Step 4: Calculate EGI. Subtract vacancy loss from GSI. $40,200 minus $2,814 equals $37,386.
Step 5: Subtract operating expenses to reach NOI. If annual operating expenses for this triplex total $14,000 (taxes, insurance, management, maintenance), then NOI equals $37,386 minus $14,000, which is $23,386.
That NOI figure is what you use to calculate cap rate and to determine how much debt the property can support. If you had skipped the vacancy deduction entirely, your NOI would have appeared as $26,200, which is roughly twelve percent higher than reality. At a six percent cap rate, that difference translates to a valuation gap of nearly $47,000. That is not a rounding error. It is a meaningful overpayment.
For a deeper look at how cap rates interact with NOI in NC markets, the cap rate calculation guide for small multifamily properties in North Carolina provides a useful companion framework.
Actual vs. General Vacancy: Why the Distinction Matters
Experienced underwriters distinguish between two types of vacancy, and conflating them is a common source of pro forma errors.
Actual vacancy reflects the current state of the property. You calculate it by multiplying the market rent of each vacant unit by twelve months. If Unit C in the triplex above is currently empty, actual vacancy is $1,050 x 12, or $12,600. This number tells you what the property is losing right now.
General vacancy is a projected percentage applied to total revenue to account for expected turnover, lease-up time between tenants, and normal market friction over a full operating year. It is forward-looking and should be grounded in local market data rather than a default assumption.
When you are underwriting a stabilized property, general vacancy is the number that belongs in your long-term NOI model. When you are evaluating a value-add deal where several units are currently offline, you need to model both: actual vacancy for the current period and a stabilized general vacancy rate for your hold period projections.
Property class also shapes which vacancy rate is appropriate. Class A stabilized properties in strong NC metros typically see vacancy in the thirty-five to forty-two percent range on a unit-level basis during repositioning phases, though stabilized operating vacancy for Class A is far lower, often three to five percent. Class B properties run slightly higher, and Class C assets higher still. For small multifamily in NC college markets, Class C vacancy can spike during summer months when student leases expire simultaneously.
How NC Market Conditions Shape Your Vacancy Assumptions
North Carolina's three major investment corridors each carry distinct vacancy dynamics that should influence how you set your assumptions.
Research Triangle (Raleigh, Durham, Chapel Hill): The Triangle continues to absorb population and employment growth driven by tech, biotech, and university anchors. Stabilized vacancy for small multifamily in core neighborhoods has remained relatively tight. However, college-adjacent submarkets near NC State and UNC Chapel Hill experience pronounced seasonal vacancy. Leases often expire in May or June, and units can sit for four to six weeks before the next academic-year tenant moves in. If you are buying near a university, your general vacancy assumption should reflect that seasonal pattern, not just the annual average. The rent growth limits in NC college towns article explores how these dynamics affect income projections more broadly.
Charlotte: Charlotte's multifamily market has seen significant new supply added at the Class A level over the past several years. That supply pressure has pushed some renters who might have moved up into new construction to stay in Class B and C product, which has actually supported occupancy in the small multifamily segment. For buyers underwriting triplexes and fourplexes in Charlotte's inner ring neighborhoods, a five to seven percent general vacancy assumption is reasonable for 2026, though you should verify with local property managers who track days-on-market for comparable units.
Triad (Greensboro, Winston-Salem, High Point): The Triad offers lower acquisition prices relative to the Triangle and Charlotte, but vacancy assumptions require more care. Some Triad submarkets have softer demand, and days-vacant between tenants can run longer than in the larger metros. A seven to ten percent general vacancy assumption is more conservative and appropriate for many Triad deals, particularly in Class C product.
One practical step that sharpens your vacancy assumption is asking a local property manager for their current days-vacant metric and average make-ready time. Pre-leasing forty-five to sixty days before a tenant's move-out date is a standard practice that compresses vacancy loss, and a manager who tracks this actively will give you better data than any published survey.
Vacancy Loss, NOI, and What It Means for Your Offer Price
NOI is the engine of multifamily valuation. Every dollar of NOI you add or subtract changes the property's implied value at a given cap rate. That relationship makes vacancy loss one of the highest-leverage inputs in your underwriting model.
The formula connecting NOI and value is:
Value = NOI / Cap Rate
If the market cap rate for a stabilized triplex in your target submarket is six percent, then every $1,000 increase in annual NOI adds roughly $16,667 to implied value. Conversely, every $1,000 you overstate NOI by using an unrealistically low vacancy assumption inflates your offer price by the same amount.
This is why buyers who underwrite conservatively on vacancy often appear to bid low relative to sellers' expectations. They are not being timid. They are pricing the asset based on income it can actually produce, not income it would produce if every unit stayed occupied every month of the year.
When you are preparing an offer, document your vacancy assumption and be ready to explain it. Sellers who have held a property for years sometimes present occupancy history that looks better than what a new owner should expect, particularly if they self-manage and have long-term tenants who have not turned over in years. Tenant turnover after a sale is common, and your vacancy assumption should account for that transition period.
If you are also thinking about how vacancy loss affects your decision to hold versus sell, the when to sell vs. refinance small multifamily in NC piece offers a useful framework for thinking through that question from the owner's side.
For buyers who want to move faster on deals without sorting through unqualified leads, FlowExit connects serious investors with vetted sellers in NC markets, so you spend less time on noise and more time on deals worth underwriting. The education here is the starting point. The lead flow is how you put it to work.