Rental Property Calculator

Rental Property Calculator

Analyze a rental property investment: net operating income, cap rate, monthly cash flow, and cash-on-cash return.

Monthly Cash Flow
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Effective monthly rental income—
Mortgage payment (P&I)—
Net operating income (annual)—
Cap rate—
Cash invested (down payment)—
Cash-on-cash return—
Disclaimer: This calculator provides estimates for general educational and planning purposes only and does not constitute financial or investment advice. It does not account for closing costs, capital expenditures, appreciation, or tax effects. Consult a real estate or financial professional before making investment decisions.

Written by Mathew | Financial Tools & Calculation Specialist · Last updated August 21, 2026

Rental Property Calculator: How to Analyze Cash Flow Before You Buy

Quick summary: A rental property calculator estimates monthly cash flow using the formula Gross Rental Income − Vacancy Allowance − Operating Expenses − Debt Service, while quick screening rules like the 1% rule and 50% rule help filter deals before running the full analysis. A good target is $100–300 in positive monthly cash flow per unit, though the 1% rule in particular has become harder to hit in many of today’s markets.

Buying a rental property based on gut feeling — or worse, just the listed rent versus the mortgage payment — is one of the fastest ways to end up with a property that quietly loses money every month. A rental property calculator solves this by running the full cash flow formula investors actually use, alongside quick screening shortcuts like the 1% and 50% rules. This guide breaks down exactly how a rental property calculator works, walks through fully worked examples, and covers where the popular shortcuts genuinely help — and where they fall short.

What Is a Rental Property Calculator?

A rental property calculator converts a potential investment’s rent, expenses, vacancy rate, and financing details into a clear cash flow figure and return percentage, so you can judge whether a property is actually a good deal before you buy it. According to Dominion Financial’s investment guidance, skipping the full calculation — or leaning only on quick rules of thumb — can make a mediocre deal look better than it actually is (dominionfinancial.com).

The Rental Property Cash Flow Formula

The standard, full formula for rental property cash flow is:

Cash Flow = Gross Rental Income − Vacancy Allowance − Operating Expenses − Debt Service

(dominionfinancial.com)

Breaking down each component:

  • Gross Rental Income — total rent expected before any deductions, plus additional income like pet rent, parking, or laundry fees
  • Vacancy Allowance — a deduction reflecting the percentage of time the unit is expected to sit unoccupied
  • Operating Expenses — property taxes, insurance, maintenance, property management fees, and other recurring cash costs (excluding mortgage principal and interest)
  • Debt Service — the full mortgage payment (principal and interest)

Landlord Studio’s guidance is explicit that depreciation should not be subtracted in this formula, since depreciation is a non-cash accounting expense — no actual dollars leave your account because of it (landlordstudio.com).

Quick Screening Rules Before the Full Calculation

Before running the complete formula on every property you consider, most investors use two shortcuts to filter out obviously weak deals.

The 1% Rule

Monthly rent should be at least 1% of the property’s purchase price

For example, a $200,000 property should generate at least $2,000/month in gross rental income to pass the 1% rule (baselane.com). Some more aggressive investors look for a 2% or even 3% rule instead — the higher the percentage, the stronger the potential cash flow, though such properties are also harder to find in most markets (calculator.net).

Importantly, several sources note the 1% rule has become significantly harder to hit in many of today’s markets, and should be treated strictly as a fast filter, not a substitute for full financial analysis (getaffordably.com; calculator.net).

The 50% Rule

A rental property’s total operating expenses will typically run around 50% of gross rental income (excluding the mortgage)

For example, if monthly rent is $2,000, the 50% rule estimates roughly $1,000/month in operating expenses — covering maintenance, vacancies, taxes, insurance, and management — leaving the other $1,000 available for the mortgage payment (permanentpto.com; calculator.net). This is a fast estimation tool, not a precise number — actual expense ratios vary significantly by property age, location, and condition (sparkrental.com).

Worked Examples

Example 1: Full cash flow calculation

A single-family rental generates $2,400/month in rent ($28,800/year gross rental income).

Step 1 — Vacancy allowance: Using the national rental vacancy rate of roughly 7.3% (Q2 2026 data): $28,800 × 0.073 ≈ $2,102

Step 2 — Net Operating Income (before debt service): $28,800 − $2,102 − operating expenses. In Dominion Financial’s worked example using this scenario, NOI after vacancy and operating expenses came to $18,784

Step 3 — Subtract debt service: $18,784 − $14,400 (annual mortgage payment) = $4,384 annual cash flow, or roughly $365/month (dominionfinancial.com)

Example 2: Applying the 1% rule to screen a property

A property is listed at $300,000. Using the 1% rule:

Minimum target rent = $300,000 × 0.01 = $3,000/month

If the property’s realistic market rent comes in well below $3,000/month, it’s a signal to dig deeper before making an offer, since it may not cash flow well without a very large down payment (fitsmallbusiness.com).

Example 3: Applying the 50% rule for a quick estimate

Monthly rent is $1,500.

Estimated operating expenses (50% rule): $1,500 × 0.50 = $750/month Remaining for mortgage payment: $750/month

If the actual mortgage payment on the property is higher than $750/month, the 50% rule flags this as a likely negative cash flow property before you even run detailed numbers (calculator.net).

Example 4: Calculating cash-on-cash return

You invest $20,000 of your own cash into a property and earn $2,000/year in net cash flow.

Calculation: Cash-on-Cash Return = (2,000 ÷ 20,000) × 100 = 10% annual yield (sparkrental.com)

What Counts as “Good” Cash Flow?

There’s no single dollar figure that qualifies as universally good cash flow, since the right target depends on rent levels, capital invested, and local market conditions. That said, a commonly cited rule of thumb from Baselane’s investor guidance is to aim for at least $100–300 per unit in monthly cash flow — below that range, the time commitment of managing vacancies, tenant maintenance, and potential evictions often outweighs the financial return (baselane.com; getaffordably.com).

For return percentages, an ROI (or cash-on-cash return) between 5% and 10% is generally considered reasonable for rental properties that include conservative cushions for repairs and vacancy, while anything above 10% is typically viewed as a strong deal (baselane.com).

Common Rental Property Calculator Mistakes

  • Relying only on the 1% or 50% rules without running full numbers. These are fast screening filters, not substitutes for a complete cash flow analysis (dominionfinancial.com; getaffordably.com).
  • Forgetting to include a vacancy allowance. Assuming 100% occupancy year-round significantly overstates real-world cash flow — most calculators recommend budgeting 8–10% vacancy to stay conservative (getaffordably.com).
  • Subtracting depreciation from cash flow. Depreciation is a paper deduction for tax purposes, not an actual cash expense — it should not reduce your calculated cash flow figure (landlordstudio.com).
  • Judging a property by raw cash flow dollars alone, without comparing it to the cash actually invested — a property producing $85/month and one producing $400/month can’t be fairly compared without factoring in how much capital each required (landlordstudio.com).
  • Ignoring property management costs even when self-managing, since your time has real value, and unexpected life changes may eventually require hiring a manager anyway.

FAQs

What is the 1% rule in real estate investing?

The 1% rule suggests a rental property’s monthly rent should be at least 1% of its purchase price. For example, a $200,000 property should rent for at least $2,000/month to pass this quick screening test.

Is the 1% rule still realistic in today’s market?

Not always — several industry sources note the 1% rule has become harder to achieve in many markets, and should be used only as a fast initial filter, not a final decision-making tool.

What’s a good monthly cash flow for a rental property?

A commonly cited benchmark is $100–300 in positive monthly cash flow per unit, though the right target ultimately depends on the market, the capital invested, and your personal risk tolerance.

Should I subtract depreciation when calculating rental property cash flow?

No — depreciation is a non-cash accounting expense used for tax purposes. Since no actual money leaves your account because of it, it should not be included in a cash flow calculation.

What’s the difference between cash flow and cash-on-cash return?

Cash flow is a raw dollar amount (income minus expenses and debt service), while cash-on-cash return expresses that cash flow as a percentage of the actual cash you invested, which makes it easier to compare properties with different financing structures.

Related Calculators

Conclusion

A rental property calculator turns rent, expenses, vacancy, and financing into the one number that actually matters: real monthly cash flow. Quick screening tools like the 1% and 50% rules are genuinely useful for filtering out weak deals fast, but they’re no substitute for running the full formula — Gross Rental Income minus Vacancy Allowance, Operating Expenses, and Debt Service — before you commit to a purchase. Whether you’re evaluating your first rental or your tenth, letting a rental property calculator do the full math protects you from the kind of optimistic assumptions that turn a promising-looking deal into a property that costs more to hold than it earns.