No rental stays occupied forever. Tenants move out, units need cleaning and repairs between leases, and finding the next tenant takes time. Some rent that’s billed never gets collected. A vacancy allowance accounts for all of this by reducing scheduled rent to something closer to what the property will actually collect over time.
It’s one of the most frequently skipped lines in rental analysis — and one of the most important, because it comes straight off the top of income.
The formula
Effective gross income = Gross scheduled rent − Vacancy & credit loss
A 5% vacancy rate on $21,600 of annual rent is $1,080 — roughly the equivalent of 0.6 months without rent each year.
Physical vacancy vs. economic vacancy
Two kinds of loss usually get bundled into one allowance:
- Physical vacancy: units that are empty. A unit vacant for one month out of twelve has about 8.3% physical vacancy for that year.
- Economic vacancy (credit loss): rent that’s charged but not collected — non-payment, concessions such as a free month, or units occupied below market rent.
Economic vacancy can be meaningful even when a property is fully occupied, so many analysts use a combined “vacancy and credit loss” allowance.
Where a vacancy rate comes from
Turnover math. One practical way to estimate vacancy is from tenancy length and time to re-lease. If tenants stay 24 months on average and each turnover leaves the unit empty for 1.5 months, vacancy is:
1.5 ÷ (24 + 1.5) = 5.9%
Market data. Local rental vacancy rates from census data, property managers or market reports give a sense of how quickly units lease in an area.
The property’s own history. For an existing rental, past rent rolls show actual vacancy and collections — often the best guide, as long as the period is long enough to include a few turnovers.
How much vacancy moves cash flow
Vacancy comes directly off income, while most expenses and the mortgage stay the same. That makes cash flow very sensitive to it.
A $1,800/month rental at different vacancy rates
Operating expenses (excluding vacancy) are $640 per month and the mortgage P&I is $950.
| Vacancy rate | Annual vacancy loss | Monthly cash flow |
|---|---|---|
| 0% | $0 | $210 |
| 3% | $648 | $156 |
| 5% | $1,080 | $120 |
| 8% | $1,728 | $66 |
| 10% | $2,160 | $30 |
| 12% | $2,592 | −$6 |
Hypothetical numbers for illustration.
Each additional percentage point of vacancy costs $18 per month here. Going from 0% to 10% cuts monthly cash flow from $210 to $30.
Break-even vacancy
A related figure is the vacancy rate at which cash flow hits zero:
For the example property, that’s 11.7%. In other words, the property could go without rent for about 1.4 months a year before cash flow turns negative — assuming everything else stays the same. A small break-even vacancy means little room for an empty month.
Turnover costs aren’t vacancy
Vacancy captures lost rent, but turnover has other costs: cleaning, paint, minor repairs, advertising, and sometimes a leasing fee. These usually belong in maintenance or a separate turnover line rather than the vacancy allowance. In the turnover example above, $1,400 per turnover spread over a 25.5-month cycle works out to about $55 per month on top of the lost rent.
What drives vacancy up or down
- Lease length. Longer leases mean fewer turnovers per year.
- Rent level relative to market. Units priced above comparable rentals take longer to fill.
- Seasonality. In many markets, summer leases fill faster than winter ones.
- Property type. Student housing, short-term and mid-term rentals have very different occupancy patterns from long-term single-unit rentals.
- Condition and management. Responsive maintenance and good screening tend to extend tenancies.
Common mistakes
Using 0% because the property is currently leased. A signed lease today doesn’t eliminate future turnover.
Applying vacancy to the wrong base. Vacancy should reduce gross scheduled income — including other income — before expenses.
Using one rate for every market. Vacancy varies widely by location and property type; a single default can be far off.
Not testing a range. Because results are so sensitive to vacancy, a table like the one above is often more useful than any single assumption.
Frequently asked questions
Is a vacancy allowance needed for a single-unit rental? Yes. A single unit is either fully occupied or fully vacant, so the allowance represents an average over several years: a month or two of turnover every couple of years, spread across every month.
What about properties with long-term tenants already in place? An existing lease reduces near-term vacancy risk but doesn’t eliminate it over a holding period. Many analysts still apply an allowance, sometimes a smaller one, to reflect eventual turnover and possible collection loss.
Should vacancy apply to other income too? Generally yes. If a unit is empty, its parking, storage or pet fees usually aren’t being collected either.
How does vacancy affect value? Because it reduces NOI, higher vacancy lowers value when value is estimated from NOI and a cap rate.
The takeaway
A vacancy allowance converts scheduled rent into realistic income by accounting for empty months and uncollected rent. It can be estimated from turnover patterns, market data or the property’s own history. Because it comes off the top of income while costs stay fixed, small changes in vacancy produce large changes in cash flow — which makes it one of the most useful inputs to stress-test.