The direct answer
Analyze a rental property by separating scheduled income, vacancy, operating expenses and financing. First calculate NOI, then after-debt cash flow, then the property and equity return ratios. A positive result is a scenario outcome, not evidence that every risk has been priced.
Start with evidence, not the asking-price story
Build an annual rent schedule from the current lease or a documented comparable-rent assumption. Include parking or laundry income separately. Decide whether the vacancy allowance covers collections and concessions as well as empty units. If the property has several units, a single average rent can obscure the impact of one expensive vacancy. Note the date and basis of each input so you can explain the estimate later.
To apply the approach to an editable scenario, use the Rental Property Calculator. For the neighboring question, explore Cap Rate Calculator.
Keep the operating and financing layers separate
Property taxes, insurance, recurring repairs and owner-paid operating costs reduce NOI. Debt service comes after NOI. This distinction lets you compare the same property under different financing assumptions without pretending that its operating performance changed. Initial rehab and acquisition cash belong in the capital invested calculation; including the same spending again as an annual operating expense would count it twice.
Use a sensitivity check before interpreting returns
Reduce rent or raise vacancy while holding the other assumptions constant. Then increase a recurring expense and observe both cash flow and return on cash. A property can have positive NOI but negative cash flow if the debt-service assumption is large. Review the source of the difference instead of relying on one attractive headline percentage. The model has no resale forecast, tax calculation or lender approval built into its annual results.
Worked example
The linked default model uses a $350,000 purchase price, $3,200 monthly rent, $100 monthly other income and 5% vacancy. Effective gross income is $37,620; after $11,409.60 of modeled operating costs, NOI is $26,210.40. Deducting $21,600 of annual debt service leaves $4,610.40, which is 5.12% of $90,000 invested cash.
Common mistakes and limitations
Do not compare one property before debt with another after debt, or mix a monthly rent input with annual costs. Review whether the maintenance allowance is ordinary repairs or capital replacement and keep that treatment consistent.
Scenario estimator based on user inputs. It is not an appraisal, lending decision, tax calculation or investment recommendation.
Frequently asked questions
Which figure should I calculate first?
Start with effective income and NOI. Financing and equity return calculations depend on that operating foundation.
Does a positive default example validate a property?
No. The example demonstrates the arithmetic. Replace the assumptions with evidence and review risks that the inputs do not capture.
Sources and further reading
The article’s examples are illustrative arithmetic. The references below provide context for operating, valuation or transaction concepts; they do not endorse the assumptions or the calculator.
- IRS — Publication 527 (2025), Residential Rental PropertyRental income and expense concepts; operating/rental expense context.
- Fannie Mae — Selling Guide B3-3.8-01, General Rental Income Information (09/02/2026)Current U.S. rental-income documentation context; comps/market rent and qualifying-income concepts.
- Office of the Comptroller of the Currency — Comptroller's Handbook — Commercial Real Estate LendingNOI, direct capitalization, cap-rate valuation and DCF concepts for commercial real estate.
Read our editorial policy for the scope of these educational methods.