Rental Property Analysis Calculator: How to Run the Numbers on Any Deal

Most people look at a rental property and do the same rough math: rent minus mortgage equals cash flow. If the number is positive, the deal looks good.

That's not an analysis. That's a guess with a subtraction problem attached.

A real rental property analysis calculator runs five metrics on every deal before you make an offer. Each metric answers a different question, and together they give you a complete picture of what you're actually buying. Here's how to run them.

The Five Metrics Every Rental Property Analysis Needs

Before we get into the math, a quick note on what you're solving for: these metrics are tools for comparison and decision-making. None of them tell you whether to buy — they tell you what the deal actually looks like so you can decide.

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1. Net Operating Income (NOI)

NOI is your starting point for every other metric. It's the income the property generates after operating expenses, before debt service.

Formula: > NOI = Gross Rental Income - Vacancy Allowance - Operating Expenses

What counts as operating expenses: property taxes, insurance, property management fees, maintenance and repairs, utilities (any you pay), landscaping, and any HOA fees. What does NOT count: your mortgage payment, depreciation, or income taxes.

Example:

• Gross rent: $24,000/year (two units at $1,000/month each)
• Vacancy allowance (5%): -$1,200
• Property taxes: -$3,200
• Insurance: -$1,400
• Management (8%): -$1,920
• Maintenance/repairs: -$2,000
• NOI: $14,280

NOI by itself doesn't tell you much — it needs to be compared to the purchase price or your invested capital. That's where the next metrics come in.

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2. Cap Rate

Cap rate measures the return the property generates on its value, independent of how you finance it. It lets you compare deals across different price points and markets on an apples-to-apples basis.

Formula: > Cap Rate = NOI / Property Value

Using our example: $14,280 / $240,000 = 5.95%

What's a good cap rate?

It depends heavily on market and property type. As general benchmarks:

• Urban/gateway markets (NYC, LA, SF): 3-5% is common — lower cap rates because appreciation expectations are higher
• Mid-size secondary markets: 5-8% is typical
• Rural or higher-risk markets: 8-12%

A cap rate of 6% in a stable secondary market is solid. A cap rate of 6% in a rural market with limited demand might not justify the risk.

Cap rate is most useful for comparing similar properties in the same market. If two duplexes in the same neighborhood have cap rates of 6.2% and 5.1%, the first is performing better relative to its price.

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3. Cash-on-Cash Return

Cap rate ignores financing. Cash-on-cash return puts it back in. It measures the return on your actual cash investment after debt service.

Formula: > Cash-on-Cash Return = Annual Pre-Tax Cash Flow / Total Cash Invested

Annual pre-tax cash flow is NOI minus your annual mortgage payments (principal and interest).

Continuing our example:

• Purchase price: $240,000
• Down payment (25%): $60,000
• Closing costs: $4,500
• Initial repairs/setup: $3,500
• Total cash invested: $68,000

Mortgage: $180,000 at 7.25% for 30 years = $1,228/month = $14,736/year

• NOI: $14,280
• Mortgage payments: -$14,736
• Annual cash flow: -$456

Cash-on-cash return: -$456 / $68,000 = -0.67%

At these numbers, the deal is slightly cash-flow negative. You're writing a small check every month and banking on appreciation. Whether that's acceptable depends on your goals — but you should know that going in, not six months after closing.

What's a good cash-on-cash return?

Most serious rental investors target 6-12%+ cash-on-cash. At today's interest rates (7%+ on investment property loans), achieving that target requires either a low purchase price relative to rents, a significant down payment, or a value-add opportunity where rents can be increased.

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4. Gross Rent Multiplier (GRM)

GRM is a quick screening tool. It tells you how many years of gross rental income it would take to pay for the property, ignoring expenses. It's not a comprehensive metric — it's a fast filter.

Formula: > GRM = Purchase Price / Annual Gross Rent

From our example: $240,000 / $24,000 = 10

A GRM of 10 means the property costs 10 times its annual gross rent. Generally:

• GRM under 8: potentially underpriced — warrants deeper analysis
• GRM 8-12: typical range for most markets
• GRM above 15: the rent-to-price ratio is unfavorable; hard to make the numbers work

GRM is useful for quickly eliminating deals before you invest time in full analysis. If you're scanning 20 listings, GRM gets you to a shortlist of 5 worth running the full numbers on.

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5. Debt Service Coverage Ratio (DSCR)

DSCR is the metric lenders use to evaluate rental property loans. It's also one of the most important signals for your own risk management.

Formula: > DSCR = NOI / Annual Debt Service

From our example: $14,280 / $14,736 = 0.97

A DSCR below 1.0 means the property doesn't generate enough income to cover its debt — you're subsidizing the mortgage from other income sources. Most DSCR lenders require a minimum of 1.0, and most want to see 1.20+ for better loan terms.

A DSCR of 0.97 is a yellow flag. The deal is not self-funding. That doesn't make it a bad investment if you believe in the appreciation trajectory or have a clear rent-increase path — but it's information you need to have.

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Putting It All Together: What the Numbers Mean

Here's how to read a completed rental property analysis:

This deal has a reasonable cap rate for its market but fails on cash-on-cash and DSCR. The right response isn't to walk away automatically — it's to figure out what would need to change for the deal to work:

• What if rents increased 10%? ($1,100/unit = $26,400 gross)
• What if you negotiated the price down to $210,000?
• What if you put 30% down to reduce debt service?

Run those scenarios through the KnowYourNut Rental Property Calculator to find the purchase price or rent level where the deal makes sense — or determine that no reasonable scenario makes it work.

Common Mistakes in Rental Property Analysis

Using optimistic vacancy rates. Many new investors use 2-3% vacancy when modeling deals. A more conservative assumption is 5-8%, and in some markets or property types, 10% is appropriate. Model conservatively; if the deal still works, buy with confidence.

Ignoring maintenance and CapEx. Newer investors budget $0-500/year for maintenance on a property that should have $2,000-4,000 budgeted. Every roof, HVAC, water heater, and appliance has a lifespan. Budget for it before you need it.

Not including management even if you self-manage. Self-managing a rental takes real time — tenant screening, lease agreements, maintenance coordination, rent collection, and legal compliance. If you value your time, model management fees even if you currently handle it yourself. This prevents a distorted ROI calculation that disappears the moment you hire help.

Using list rent, not achieved rent. A landlord listing at $1,100 doesn't mean the market bears $1,100. Check what comparable units are actually renting for and how quickly they're being absorbed. If units sit vacant for 30-60 days between tenants, factor that into your vacancy assumption.

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Use the KnowYourNut Rental Property Calculator to run a full five-metric analysis on any deal in about 10 minutes. Plug in your numbers and see cap rate, cash-on-cash, NOI, GRM, and DSCR side by side — plus a cash flow projection and the purchase price where the deal hits your target return.

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*This content is for informational purposes only and does not constitute financial advice. Real estate investing involves risk, including the possible loss of principal. Market conditions, interest rates, and local regulations vary and can materially affect investment outcomes. Consult a qualified financial advisor or real estate professional before making any investment decision.*