Applicability: United States rental planning; amounts are in USD. Editorial review: 2026-09-25. Fictional examples demonstrate the calculator, not expected rental performance.
Outcome
Estimate recurring cash after vacancy, operating expenses, financing and reserves. Understand which input change would make a rental scenario stop meeting your needs.
Before you begin
Prepare a monthly rent assumption, vacancy percentage, operating expenses, financing payment, reserves and total cash invested. Keep the rent evidence and expense estimates dated. The free calculator does not verify that a property may be rented or that a tenant will pay the assumed rent.
Use monthly figures for every recurring amount. Cash invested is the total cash committed to the investment, not the monthly payment or the full purchase price financed by someone else. Calculation works without an account; saving requires a verified account.
Practical steps
- Open Rental cash flow. Enter Monthly scheduled rent before vacancy, and set the Vacancy assumption.
- Enter Monthly operating expenses. Include taxes, insurance, management, maintenance, utilities and association costs where applicable. Convert annual estimates to monthly amounts first.
- Enter Monthly financing payment separately. Include the required payment rather than just interest if principal is also payable, and avoid duplicating expenses already included in that payment.
- Enter Monthly reserves and Total cash invested. Keep the reserve assumption separate from costs already included in operating expenses.
- Choose Calculate scenarios. Read effective rent, net operating income, monthly cash flow, annual cash flow and cash-on-cash return together.
- Name and save the result. Recalculate with lower rent or higher vacancy and expenses, then save a distinct snapshot for that assumption set.
Worked example
A fictional rental has scheduled rent of $2,000 per month and 5% vacancy. Effective rent is $1,900. Subtract $600 operating expenses to obtain $1,300 monthly net operating income. Subtract $900 financing and $150 reserves to obtain $250 monthly cash flow, or $3,000 annually.
With $60,000 cash invested, cash-on-cash return is 5%. Raising vacancy to 10% reduces effective rent to $1,800, monthly cash flow to $150 and cash-on-cash return to 3%. This example changes one input so the effect is easy to see; actual downside conditions can affect several inputs at once.
How to interpret it
Net operating income excludes financing and reserves in this model. Cash flow subtracts both. Cash-on-cash return divides annual cash flow by cash invested; it does not include appreciation, income taxes or proceeds from a sale.
Annual cash flow is the monthly estimate multiplied by twelve. It is not a month-by-month forecast of lease-up, seasonal demand, repairs or financing changes. Vacancy-adjusted rent is rounded to the nearest cent, with half cents rounded up.
A positive number can coexist with missing rental licensing, occupancy, condition or HOA evidence. Resolve those questions independently. A reserve is a cash-planning input, not a statement about tax treatment.
Common problems
- Cash-on-cash unavailable: the calculator cannot compute that percentage when cash invested is zero. Enter the actual investment if known.
- Result looks too favorable: check annual-versus-monthly amounts, vacancy, repairs, management and double-counted or omitted costs.
- Unknown expense: the free calculator requires numeric inputs. Label any planning estimate in your own notes; in a research brief, unknown amounts can remain blank.
- One good scenario treated as a forecast: test a downside case and verify the rent evidence before relying on the result.
Next action
Use What to verify before making an offer for rental due diligence. Read Compare scenarios for the assumptions and saved versions in an investment research report.