The 7 Numbers That Tell You If a Rental Property Is Worth Buying
You've found a property. It looks good on the surface, the neighborhood seems solid, and you like the owner's asking price. But before you sign the dotted line, you need to know something that the real estate agent won't tell you: whether this deal actually pencils.
The difference between a profitable rental and a money-draining liability comes down to seven metrics. These numbers tell you whether you're buying an asset or a problem. Let's walk through each one with real math so you can evaluate your next opportunity with confidence.
Metric 1: Rental Yield (Return on Revenue)
The Formula:
Rental Yield = (Annual Gross Rent / Purchase Price) × 100
What It Means: Rental yield shows the gross annual income your property generates as a percentage of what you paid for it. It's the simplest return metric—but it's also incomplete, since it doesn't account for expenses or debt.
Worked Example:
- •Purchase price: $180,000
- •Monthly rent: $1,500
- •Annual gross rent: $1,500 × 12 = $18,000
- •Rental yield = ($18,000 / $180,000) × 100 = 10%
What's Good?
- •Below 5%: Walk away. You're in a high-price, low-rent market where appreciation is your only hope—that's speculation, not investing.
- •5–8%: Acceptable. You're in a middle-of-the-road market. Expect moderate returns.
- •8%+: Strong. Your income is outpacing your capital, which means cash flow matters on day one.
Why This Matters: Use as your first filter. Properties under 5% gross yield typically don't work after expenses.
Metric 2: Cap Rate (Net Operating Income Return)
The Formula:
Cap Rate = (NOI / Purchase Price) × 100
Where NOI = Annual Gross Rent − Annual Operating Expenses
What It Means: Cap rate is the rental yield's more sophisticated cousin. It subtracts actual operating expenses (maintenance, property tax, insurance, management, vacancy) to show your true annual return on the property itself—before financing.
Worked Example:
- •Annual gross rent: $18,000
- •Annual operating expenses (estimated at 45% of gross rent): $8,100
- •Property tax: $2,200
- •Insurance: $1,200
- •Maintenance & repairs: $2,400
- •Property management: $1,800
- •Vacancy allowance (8% of rent): $1,440
- •Other expenses (utilities landlord-paid, etc.): −$940
- •NOI = $18,000 − $8,100 = $9,900
- •Cap rate = ($9,900 / $180,000) × 100 = 5.5%
What's Good?
- •Below 4%: Weak. You're betting on appreciation or financing tricks. Pass.
- •4–6%: Fair. Solid middle-market return. Expect steady income with modest upside.
- •6%–8%+: Excellent. You're extracting real value from day one.
Why This Matters: Cap rate strips out debt to show what the property itself generates. Low cap rates signal expensive, risky markets. High cap rates indicate buyer's markets.
Metric 3: Cash-on-Cash Return (What You Pocket Annually)
The Formula:
Cash-on-Cash Return = (Annual Cash Flow / Total Cash Invested) × 100
Where Annual Cash Flow = NOI − Annual Debt Service
What It Means: This is the real payoff—the annual cash you actually put in your pocket as a percentage of the capital you deployed. It accounts for mortgage payments, so it's the metric that tells you whether this deal cash-flows on day one.
Worked Example:
- •NOI: $9,900 (from above)
- •Purchase price: $180,000
- •Down payment (assume 20%): $36,000
- •Loan amount: $144,000
- •Loan terms: 30-year mortgage at 7% interest
- •Annual debt service (mortgage P&I): $10,109.27
- •Annual cash flow = $9,900 − $10,109.27 = −$209.27 (negative cash flow)
- •Cash-on-cash return = (−$209.27 / $36,000) × 100 = −0.58%
What's Good?
- •Negative: The property doesn't cash flow. You lose money every month.
- •0–3%: Barely breaks even. Every dollar counts.
- •4–8%: Solid returns. You're building equity and pocketing cash.
- •8%+: Exceptional. This is a rare find in today's market.
Why This Matters: This is where fantasy meets reality. Many "deals" look good until you factor in the mortgage. If a property doesn't cash flow, you're betting on appreciation—investor roulette.
Metric 4: DSCR – Debt Service Coverage Ratio
The Formula:
DSCR = NOI / Annual Debt Service
What It Means: DSCR tells you how comfortably the property covers its debt obligations. Lenders love this metric—it shows them your safety margin. A DSCR of 1.25 means the property generates $1.25 in NOI for every $1 of debt service.
Worked Example:
- •NOI: $9,900
- •Annual debt service: $10,109.27
- •DSCR = $9,900 / $10,109.27 = 0.98
What's Good?
- •Below 1.0: You can't cover the mortgage from rental income. Risky.
- •1.0–1.25: Tight. You're covering debt, but with no cushion for expenses or vacancy surprises.
- •1.25–1.5: Healthy. Most lenders require this minimum.
- •1.5+: Strong. You have room to absorb income drops or expense spikes.
Why This Matters: DSCR below 1.0 means you can't cover debt from rental income. You'll need reserves to cover shortfalls. This separates true investments from speculation.
Metric 5: Gross Rent Multiplier (GRM)
The Formula:
GRM = Purchase Price / Annual Gross Rent
What It Means: Quick valuation tool for comparing properties in the same market. Lower is better.
Worked Example:
- •Purchase price: $180,000
- •Annual gross rent: $18,000
- •GRM = $180,000 / $18,000 = 10
What's Good?
- •Below 8: Strong deal. You're buying rental income at a discount.
- •8–10: Fair market. Neither cheap nor expensive.
- •10–12: Pricey. You're paying a premium.
- •Above 12: Expensive. Likely in a high-appreciation market; cash flow will be tight.
Why This Matters: GRM is a market sanity check. If comparable properties trade at 8-10 but yours is 12, ask why. Premium location? Or overpriced? Benchmark against comps.
Metric 6: Vacancy Rate (And How to Factor It In)
The Formula:
Effective Gross Income = Annual Gross Rent × (1 − Vacancy Rate)
Then use Effective Gross Income to recalculate Cap Rate and Cash Flow.
What It Means: Vacancy is the rent you don't collect because units sit empty. Beginners often assume 100% occupancy. Pros assume 5–10% vacancy depending on the market. Your operating expense calculations should reflect real-world vacancy.
Worked Example:
- •Annual gross rent (100% occupancy): $18,000
- •Market vacancy assumption: 8%
- •Expected vacancy loss: $18,000 × 0.08 = $1,440
- •Effective gross income: $18,000 − $1,440 = $16,560
If we recalculate NOI with this vacancy assumption:
- •Effective gross income: $16,560
- •Operating expenses (now 45% of effective income): $7,452
- •NOI (accounting for vacancy): $16,560 − $7,452 = $9,108
- •Revised cash flow: $9,108 − $10,109.27 = −$1,001.27 (worse)
What's Good?
- •3–5% vacancy: Strong market. High demand, quick turnover.
- •5–8% vacancy: Normal market. Standard assumption for acquisitions.
- •8–12% vacancy: Soft market. Watch out.
- •Above 12%: Struggling market. Deal may not work.
Why This Matters: Vacancy isn't theoretical—it's cash out of your pocket. Always model for it. If you assume 0% and hit 8%, your deal collapses.
Metric 7: Price-to-Rent Ratio (Valuation Compass)
The Formula:
Price-to-Rent Ratio = Purchase Price / Annual Gross Rent
What It Means: This is GRM's cousin—it's the inverse. A lower ratio means you're buying more rent per dollar spent. It's used to spot whether a market is overheated or undervalued.
Worked Example:
- •Purchase price: $180,000
- •Annual gross rent: $18,000
- •Price-to-Rent Ratio = $180,000 / $18,000 = 10
(This is the reciprocal of GRM, so 10 means you're paying $10 for every $1 of annual rent.)
What's Good?
- •Below 10: Undervalued. Buying power relative to income is high.
- •10–15: Fair market. In equilibrium.
- •15–20: Overvalued. Rent growth is priced in; cash flow will lag.
- •Above 20: Bubble territory. Be cautious.
Why This Matters: High price-to-rent ratios signal overheated markets. If your market is at 20 while national average is 15, rents won't catch up soon. Know your market's ratio.
Summary Table: The 7 Numbers at a Glance
| Metric | Formula | Example Result | What's Good? | Action |
|---|---|---|---|---|
| Rental Yield | (Annual Rent / Price) × 100 | 10% | 8%+ | If below 5%, pass |
| Cap Rate | (NOI / Price) × 100 | 5.5% | 6%+ | If below 4%, risky |
| Cash-on-Cash | (Annual Cash Flow / Cash Down) × 100 | −0.58% | 4%+ | If negative, needs work |
| DSCR | NOI / Annual Debt Service | 0.98 | 1.25+ | If below 1.0, underfunded |
| GRM | Price / Annual Rent | 10 | 8–10 | If above 12, expensive |
| Vacancy | Model as % of gross income | 8% assumed | 5–8% market | Factor into all calcs |
| Price-to-Rent | Price / Annual Rent | 10 | 10–15 | If above 20, caution |
The Bottom Line
These seven numbers tell you if a deal works. Run them on every prospect. Those that pass deserve deeper due diligence. Those that fail? Move on. Winning investors say "no" fast to bad deals.
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