Rental Property Cash Flow Calculator — Cap Rate, Cash-on-Cash & Monthly Income
Learn exactly how much a rental property puts in your pocket each month. This guide explains net operating income, cap rate, cash-on-cash return, and the 50% rule — then shows you how to model it in seconds.
A rental property cash flow calculator answers the only question that matters to a landlord: after every bill is paid, does the property send you a check or a bill? Positive monthly cash flow is the difference between a wealth-building asset and a second job you pay for. This guide walks through the math, the benchmarks real estate investors actually use, and the mistakes that make a "cash-flowing" deal go negative.
What Is Rental Cash Flow?
Monthly cash flow is the money left after you collect rent and pay every expense tied to the property, including the mortgage. The core formula is simple:
Monthly Cash Flow = Effective Rental Income − Operating Expenses − Debt Service (mortgage P&I)
"Effective" rental income deducts vacancy and credit losses. "Operating expenses" includes taxes, insurance, maintenance, management, and reserves — but not the mortgage principal. Debt service is paid separately, which is why a property can have strong net operating income (NOI) yet weak cash flow if the loan is expensive.
Step 1 — Gross Scheduled vs. Effective Rent
Start with Gross Scheduled Rent (GSR): the rent you'd collect if the unit were occupied 12 months a year. Then subtract vacancy. The national average vacancy rate is about 8% (NMHC 2024), but it swings from under 4% in tight Sun Belt markets to double digits in weak ones.
| Metric | Example (3BR SFR) |
|---|---|
| Monthly rent | $1,950 |
| Vacancy allowance (8%) | −$156 |
| Effective rental income | $1,794 |
Many first-time landlords skip vacancy and then wonder why a one-month empty turnover wipes out a year of "profit." Always model at least 5–8%.
Step 2 — Operating Expenses
Operating expenses are everything except the mortgage. A useful shortcut is the 50% rule: operating costs (excluding debt) run about half of gross rent for a typical single-family rental. Our example property carries:
- Property taxes: $237/month
- Insurance: $120/month
- Maintenance reserve: $150/month
- Property management (10%): $195/month
- Capital-expense (Capex) reserve (5%): $98/month
That totals roughly $800/month in operating expenses — close to the 50% rule estimate of $975. The gap is healthy; it means this property is better than average on costs.
Step 3 — Debt Service
A 25% down payment on a $285,000 home is $71,250. At 7.0% on a 30-year loan, the principal-and-interest payment is about $1,510/month. Subtract that from effective income less operating expenses:
| Line | Amount |
|---|---|
| Effective rental income | $1,794 |
| Operating expenses | −$800 |
| NOI | $994 |
| Mortgage P&I | −$1,510 |
| Monthly cash flow | −$516 |
This example does not cash flow — a common result in high-price markets. That is not a failure of the calculator; it is the calculator doing its job and telling you the truth before you close.
Cap Rate vs. Cash-on-Cash
Two ratios summarize a deal, and investors confuse them constantly.
Cap Rate
Cap Rate = NOI ÷ Property Price. It measures the asset's return ignoring financing, so you can compare a $100,000 cash purchase to a leveraged one. Our property: NOI $994 × 12 = $11,928 ÷ $285,000 = 4.2%. The national median is about 5.5% (NMHC/CoStar 2024), so this is a below-median cap rate — typical for an expensive coastal-style market.
Cash-on-Cash Return
Cash-on-Cash = Annual Pre-Tax Cash Flow ÷ Total Cash Invested. Here you'd need positive cash flow first; with −$516/month the return is negative. When a deal does flow, this is the number your lender and partners care about because it reflects your actual out-of-pocket yield.
The 1% and 50% Rules as Screeners
Before building a full model, two back-of-envelope checks save time:
- 1% rule: monthly rent ≥ 1% of purchase price. $285,000 × 1% = $2,850; our $1,950 rent fails. In the Midwest and South, 1%+ is common; in coastal markets 0.7–0.8% is the new normal.
- 50% rule: operating expenses ≈ 50% of rent. Useful for a 30-second sanity check, never a final answer.
Why Location Changes Everything
The same $1,950 rent in Dayton, Ohio (median home price ~$150,000) clears $400+/month. In a $285,000 market it loses money. That is why our state-by-state guides matter: property tax rates alone range from 0.28% (Hawaii) to 2.44% (New Jersey). The calculator below lets you test your exact numbers.
Common Cash Flow Mistakes
- Ignoring Capex. Roofs, HVAC, and water heaters fail on a schedule. Budget 5–10% of rent.
- Underestimating management. Even if you self-manage now, price it in — you may not want to forever.
- Using list rent, not achievable rent. Pull comparable listings, not Zillow guesses.
- Forgetting turnover costs. Paint, cleaning, and lost rent between tenants add up.
Using the Calculator Below
Enter purchase price, down payment, loan terms, rent, and expenses. The tool computes NOI, cap rate, cash-on-cash, and monthly cash flow instantly — entirely in your browser. Nothing is uploaded; you can save scenarios and compare them side by side. Start with the sample data, then overwrite it with your deal.
Disclaimer: This calculator provides estimates for education only. It is not tax, legal, or financial advice. Confirm figures with a licensed CPA and real estate professional before purchasing.
Contact & corrections
RentalInvestCalc is an independent editorial project. Spot a data error or want a source added? Email 18999737@qq.com or read our About page. We publish estimates and guides, not tax, legal, or financial advice — always confirm figures with the county assessor and a licensed CPA or attorney.