Calculator guide
Rental Property Calculator
A real analysis goes beyond rent minus mortgage. This guide walks through how income, expenses, financing, and reserves all factor into the full picture.
What the metric means
A real analysis goes beyond rent minus mortgage. This guide walks through how income, expenses, financing, and reserves all factor into the full picture.
DealPrism treats the rental property calculator as the full decision-support layer, surfacing cash flow, cap rate, cash-on-cash return, DSCR, and downside scenarios under the current assumptions.
Formula and variables
Where:
- Rent + Other Income
- Gross scheduled income from all sources
- Vacancy
- Estimated lost income from vacancies (typically 5–10% of gross rent)
- Operating Expenses
- Management, maintenance, CapEx reserves, taxes, and insurance
- Monthly Debt Service
- Principal and interest payment on the loan
Example:
- Rent = $2,200/month
- Vacancy (5%) = $110/month
- Effective income = $2,200 − $110 = $2,090
- Operating expenses = $620/month
- Debt service = $1,320/month
- Step 1: Cash Flow = $2,090 − $620 − $1,320
- Step 2: Cash Flow = $150/month
A $150/month cash flow means the property stays in the black under current assumptions, with modest margin for minor cost increases.
What strong vs weak results usually mean
Stronger result: A useful rental property analysis shows the full stack: income, vacancy, operating expenses, financing, and return metrics together. If one output looks good but the rest look fragile, the deal is not truly healthy.
Weaker result: A weak analysis usually hides assumptions. If taxes, insurance, vacancy, maintenance, CapEx, or closing cash are missing, the result may look better on paper than it will perform in reality.
- Use real rent comps instead of listing optimism.
- Model management, maintenance, CapEx, taxes, and insurance explicitly.
- Check both cash flow and DSCR before deciding the deal is safe.
Example analysis
If a property rents for $2,200/month and lands at $1,725 effective income after vacancy, then the loan, taxes, insurance, management, maintenance, and CapEx reserves decide whether the deal stays positive.
This is the point of an underwriting calculator: one number should always be traceable back to its underlying assumptions. If the output changes after a small rent, expense, or financing update, that is not noise. It is the deal showing you where the real sensitivity lives.
Common mistakes
- Comparing only rent and mortgage payment.
- Skipping vacancy, management, maintenance, or CapEx reserves.
- Using listing taxes or rent without validating local comps.
Related FAQs
Related resources
Why this metric should not stand alone
No serious rental property decision should rely on a single output. A cap rate without financing context, a mortgage payment without operating expenses, or a DSCR without rent validation can all point investors in the wrong direction.
The practical goal is not to memorize formulas. It is to understand which assumption changed, whether that change is realistic, and how the full deal behaves once the inputs are connected.
Analyze your own deal
See this metric in context with your purchase price, rent, expenses, and financing assumptions.
Analyze your own dealDealPrism provides educational analysis based on available data and user assumptions. Results are estimates and may change if rent, taxes, insurance, financing, or other inputs are updated. This content is not financial, legal, tax, or investment advice.