How to Analyze a Rental Property: Cap Rate and Cash Flow

The Four Key Metrics

1. Cap Rate (Capitalization Rate)

Formula: Net Operating Income (NOI) ÷ Purchase Price

Example: $300,000 duplex

• Gross rent: $2,000/month = $24,000/year

• Vacancy (5%): -$1,200

• Maintenance (10% of rent): -$2,400

• Property taxes: -$3,000

• Insurance: -$600

• NOI: $16,800/year

• Cap rate: $16,800 ÷ $300,000 = 5.6%

Interpretation:

• A 5.6% cap rate means the property yields 5.6% a year on the purchase price, before any mortgage and before income tax
• The comparison that matters is against the 10-year Treasury on the day you buy, because that is the risk-free alternative. A cap rate that is only a point or two above the current 10-year is paying you very little for illiquidity, tenants, vacancy and a roof
• 5.6% is okay, not great — and as the next section shows, it is not enough to carry debt at today's rates

Run your own numbers first: the cap rate calculator does the NOI build and the division in one pass, which matters because almost every mistake in this whole article happens inside NOI, not inside the division.

Good cap rate zones (2026):

• Below 4%: Overpriced (avoid)
• 4-5%: Fair, depends on market appreciation
• 5-7%: Good for income
• 7-10%: Excellent cap rate (need to understand WHY it's so high—could be risky property)

2. Cash-on-Cash Return

Formula: Annual Cash Flow ÷ Down Payment

Same duplex example:

• NOI: $16,800

• Mortgage payment (80% LTV @ 6.5%, 30 years — a $240,000 loan at $1,517/month): -$18,204

• Annual cash flow: -$1,404

• Down payment: $60,000 (20%)

• Cash-on-cash return: -$1,404 ÷ $60,000 = -2.3%

Interpretation:

• You put in $60K and the property costs you about $1,400 a year to hold
• A 5.6% cap rate cannot carry a 6.5% mortgage at 80% leverage. The debt is more expensive than the asset yields, so the gap comes out of your pocket every month
• This deal reaches break-even cash flow at roughly 26% down ($78,500) and only earns a positive cash return above that
• The 5.6% cap rate did not change. Leverage is what turned a modest return into a negative one, which is exactly why cap rate alone never decides a purchase

Minimum acceptable: 3-5% cash-on-cash

Cash-on-cash is also the metric that changes most when you change the deal, so it is worth solving backwards: fix the down payment you can actually afford and see what rent the property needs to clear break-even, or fix the rent and see what down payment it takes. The real estate ROI calculator will run both directions, including the appreciation and principal-paydown components that cash-on-cash deliberately ignores.

3. Price-to-Rent Ratio

Formula: Purchase Price ÷ Annual Rent

Same duplex:

• Price: $300,000
• Annual rent: $24,000
• Price-to-rent: $300,000 ÷ $24,000 = 12.5

Interpretation:

• You're paying 12.5 years of rent to own it
• Below 15: Generally good (property is reasonably priced)
• Above 20: Overpriced (rent won't justify purchase)
• 15-20: Depends on local market

4. Debt Service Coverage Ratio (DSCR)

Formula: NOI ÷ Annual Debt Payments

Same duplex:

• NOI: $16,800
• Annual debt service (mortgage): $18,204
• DSCR: $16,800 ÷ $18,204 = 0.92

Interpretation:

• The property covers 92% of its own debt payments. You fund the rest
• A rent drop hurts DSCR by more than the drop itself, because property tax and insurance do not fall with the rent. Cut gross rent 30% to $16,800 and NOI falls to about $10,700 after the same fixed costs — DSCR goes from 0.92 to roughly 0.59, a 36% fall in coverage from a 30% fall in rent. That gap is operating leverage, and it is the single most under-modelled risk in a rental spreadsheet
• Minimum acceptable: 1.2 (most lenders require 1.25+)
• Ideal: 1.5+
• At 20% down this deal does not finance. A lender sizing to 1.25 allows $13,440 of annual debt service, which supports a loan of about $177,000 — a 41% down payment on a $300,000 purchase

DSCR is also the number the lender underwrites to rather than your income, so it decides whether the deal is financeable at all before it decides whether it is good. Size the maximum loan your NOI actually supports with the DSCR loan calculator before you make an offer — finding out at underwriting that you need another $60,000 of cash is an expensive way to learn it.

Evaluating 5 Properties (Case Study)

Property 1: Urban Multifamily

• Price: $500K, 4-unit
• Rent: $2,200/unit = $8,800/month
• Gross rent: $8,800 × 12 = $105,600
• Vacancy: -$5,280
• Maintenance: -$10,560
• Taxes: -$5,000
• Insurance: -$2,000
• NOI: $82,760
• Cap rate: $82,760 ÷ $500K = 16.6%

Verdict: the listing is wrong, not the deal. Cap rate is a ratio, so an impossible one means an impossible input. Run the price-to-rent check on the same figures: $500,000 ÷ $105,600 = 4.7, against the 12-15 a healthy purchase shows. Nothing legitimate rents for a fifth of its price every year. Either the rent roll counts units that are vacant or below-market leases that expire, or the price excludes something — deferred maintenance, an assessment, a land lease. Get the actual signed leases and the last two years of operating statements before you believe any of these numbers.

Property 2: Suburban SFR

• Price: $350K, single family
• Rent: $2,000/month
• NOI: $20,000 (after all expenses)
• Cap rate: $20K ÷ $350K = 5.7%
• Down payment (20%): $70K
• Mortgage: $280,000 at 6.5% over 30 years = $21,237/year
• Cash-on-cash: ($20,000 - $21,237) ÷ $70,000 = -1.8%
• DSCR: 0.94

Verdict: a good asset that this financing cannot carry. The 5.7% cap rate is genuinely fine for 2026 and the property is not overpriced. But 80% leverage at 6.5% costs more than the property yields, so it bleeds about $1,200 a year and no lender underwriting to 1.25 DSCR will write the loan. It works at roughly 25% down ($86,300), where cash flow reaches break-even. Same building, different capital stack, opposite answer.

Property 3: Overpriced City

• Price: $600K, SFR in trendy city
• Rent: $2,200/month = $26,400/year
• Expenses: $8,000/year
• NOI: $18,400
• Cap rate: $18,400 ÷ $600K = 3.1%

Verdict: Overpriced. Buying for appreciation only (risky).

Property 4: Cheap Rural

• Price: $150K, duplex
• Rent: $800/unit = $1,600/month
• Expenses: $300/month
• NOI: $15,600
• Cap rate: $15,600 ÷ $150K = 10.4%

Verdict: Excellent cap rate, but understand WHY it's cheap. Crime? Bad schools? Take the 10% return if local economy is growing.

Property 5: Positive Cash Flow

• Price: $400K, 3-unit
• Rent: $2,500/unit = $7,500/month
• Expenses: $2,000/month
• NOI: $66,000/year
• Cap rate: $66K ÷ $400K = 16.5%

Verdict: same failure as Property 1, and the same test catches it. Price-to-rent is $400,000 ÷ $90,000 = 4.4, and the 16.5% cap rate trips the page's own red flag at 12%. Two independent metrics computed from the same inputs both say the inputs are unreal. When that happens, stop analyzing and go verify the source data — a spreadsheet cannot tell you a rent roll is fiction, but a ratio this far out of range always means one of the two numbers you fed it is wrong.

The Red Flags

Red flag 1: Cap rate > 12%

• Why is it so high? Market collapse? Crime area? Bad condition?
• Don't buy without understanding

Red flag 2: Cap rate < 3%

• Buying on appreciation hope only (risky)
• No income cushion

Red flag 3: Price-to-rent > 25

• Price is too high relative to rent
• Rents would need to spike 50%+ for math to work

Red flag 4: DSCR < 1.2

• Little cushion if rents drop
• Risky

Red flag 5: Vacancy assumed at 0%

• Unrealistic
• Use 5-10% vacancy assumption

The Numbers That Matter

Go, no-go decision points:

Read the columns together, not separately. The duplex at the top of this article sits in the "Consider" row on cap rate and in the "SKIP" row on cash-on-cash, because 80% leverage at 6.5% is more expensive than a 5.6% asset yield. When two columns disagree, the financing is usually what is disagreeing with them.

Building Your Analysis Spreadsheet

Create a simple Excel sheet:

1. Property address
2. Purchase price
3. Down payment %
4. Mortgage amount
5. Mortgage rate and term
6. Gross annual rent
7. Vacancy %
8. Maintenance %
9. Property tax
10. Insurance
11. NOI
12. Cap rate
13. Cash-on-cash return
14. DSCR

Calculate all metrics. If not in the "BUY" zone, skip property.

The 1% Rule (Quick Filter)

Rule: Monthly rent should be at least 1% of purchase price.

Example:

• Property $300K
• 1% = $3,000/month minimum rent
• If rent is $2,500, fail the test
• If rent is $3,200, pass the test

This is a rough filter. Use detailed analysis for final decision.

FAQ

What expenses does NOI leave out, and why does that matter?

NOI excludes the mortgage — that is deliberate, so cap rate describes the property rather than your financing. But most beginner spreadsheets also leave out three real costs: property management (typically 8–10% of collected rent, and you should include it even if you self-manage, because your time is not free and you may not always be able to give it), capital expenditure reserves for the roof, HVAC, water heater and appliances, which are not "maintenance" and are usually budgeted separately at 5–10% of rent, and leasing costs each time a tenant turns over. Add management at 10% of collected rent ($2,280) and a capital reserve at 8% of gross rent ($1,920) to the $300,000 duplex above, and its $16,800 NOI falls to $12,600 — turning a 5.6% cap rate into 4.2%. Nothing about the building changed; the first number was simply incomplete.

Is a high cap rate good or is it a warning?

Both, and the ratio itself cannot tell you which. Cap rate is a yield, and yield compensates for risk. A 10% cap rate in a growing small city with stable tenants is a genuinely good buy. The same 10% in a shrinking market, a high-crime block, or a building with a failing roof is the market pricing in the risk correctly. Anything above 12% should be treated as a data error until proven otherwise — as the two 16% examples above show, an impossible ratio almost always means one of the two inputs is fiction. Get the signed leases and two years of operating statements before you believe a headline number.

How much does vacancy actually cost me?

More than the vacancy percentage suggests, because fixed costs continue while rent stops. A 5% vacancy assumption on $24,000 of rent is $1,200 of lost income, but the property tax, insurance and mortgage keep running through the empty month, so the whole $1,200 comes straight out of cash flow. On a deal already running at −$1,404 a year, one extra vacant month adds another $2,000 of drawdown. The general rule: the thinner the cash flow, the more damage each vacant month does, which is why 3–5% cash-on-cash is a floor and not a target.

Does appreciation make a negative-cash-flow deal worth buying?

Sometimes, but you should be honest that you are then buying a leveraged bet on prices, not an income asset. A negative-cash-flow property requires you to fund it every month out of other income, for as long as you own it, and you cannot sell a portion of it if that income stops. If the case for a deal rests on appreciation, ask two questions: how many months of negative cash flow can you fund if you lose your job, and what happens to your equity if prices are flat for five years while you feed it? The cap rate and DSCR tests exist precisely to stop appreciation optimism from being the only thing holding a deal up.

What does depreciation do to the numbers?

It improves the after-tax return without changing cash flow. Residential rental buildings are depreciated over 27.5 years on a straight-line basis, on the building value only — land is not depreciable. On a $300,000 purchase with, say, $240,000 allocated to the building, that is roughly $8,700 a year of paper deduction against rental income. It is not free: depreciation reduces your basis, and on sale the amount claimed is recaptured at a rate of up to 25% under §1250. Treat it as a deferral that improves your holding-period cash-after-tax, not as a reason a bad deal is secretly good.

Sources

• IRS Publication 527, Residential Rental Property — deductible operating expenses, the 27.5-year residential recovery period, and the land/building allocation.
• IRS Publication 544, Sales and Other Dispositions of Assets — §1250 unrecaptured gain and the 25% maximum rate on depreciation recapture.
• Freddie Mac Primary Mortgage Market Survey — the published weekly mortgage rate series to check the financing assumptions in this article against the day you are actually buying.
• US Treasury daily yield curve rates — the 10-year Treasury yield, the risk-free benchmark a cap rate should be measured against.
• US Census Bureau, Rental Vacancy Rates (Housing Vacancies and Homeownership survey) — national and regional vacancy data for sanity-checking a vacancy assumption.