The Only 3 Numbers You Need to Evaluate a Rental Deal (And 5 That Are Distractions)

What Are the 3 Most Important Numbers for Evaluating a Rental Property?

Cap rate, cash-on-cash return, and the 1% rule are the only three metrics a rental investor needs. Together, they answer the three questions that determine whether a deal works: "Is the price reasonable?" (cap rate), "What do I actually earn on my money?" (cash-on-cash), and "Should I even run the full math?" (1% rule).

Here is how the three metrics work together on a $300,000 property with $2,000/month rent and $75,000 down payment (25%):

Table: Three essential metrics applied to a $300,000 rental property with $2,000/month rent (Source: NAR, NAA).

Regarding the three essential metrics, the 1% rule fails immediately — the rent is too low relative to the price. The cap rate is marginal at 4.8% (below the 5% minimum for a good deal). Only cash-on-cash passes at 8%, and that depends heavily on financing terms. A deal that fails 2 of 3 tests is a weak deal.

Essential metrics: 1% rule = quick filter. Cap rate = unlevered profitability. Cash-on-cash = actual return on invested cash. Two of three must pass for a deal to work (Source: NAR, BiggerPockets).

Why Are Gross Yield and ROI Misleading for Rental Properties?

Five commonly cited metrics add complexity without improving investment decisions. Each one has a specific flaw that makes it unreliable for deal evaluation:

1. Gross Yield. Gross yield divides annual rent by purchase price without subtracting any operating expenses. A property with a 10% gross yield in New Jersey (property tax 2.4%) produces dramatically different net returns than a 10% gross yield property in Colorado (property tax 0.5%). Gross yield makes high-expense markets look equivalent to low-expense markets.

2. Internal Rate of Return (IRR). IRR projects multi-year returns including appreciation assumptions, sale price estimates, and refinancing scenarios. These projections require guessing future market conditions 5–10 years out. NAR data shows that 5-year home price projections miss actual outcomes by 15–40%. IRR is a planning tool, not a decision tool.

3. Gross Rent Multiplier (GRM). GRM divides purchase price by annual gross rent. A $300,000 property with $24,000 annual rent has a GRM of 12.5. But GRM ignores expenses, financing, vacancy, and market-specific costs. Two properties with identical GRM can have vastly different cash flows.

4. Return on Investment (ROI). ROI is undefined for rental properties because investors disagree on what counts as "return." Does it include appreciation? Mortgage paydown? Tax savings? Depreciation benefits? Different ROI calculations produce results ranging from 5% to 40% on the same property.

5. Cash Flow Per Unit. Cash flow per unit is a portfolio management metric, not a deal evaluation metric. A duplex with $200/month per unit might outperform a single-family home with $300/month total because the duplex spreads risk across two tenants.

Regarding misleading metrics, the problem is not that these numbers are wrong — it is that they are incomplete. Gross yield ignores expenses. IRR requires predictions. GRM ignores financing. ROI has no standard definition. Cash flow per unit is portfolio-level. The three essential metrics (cap rate, CoC, 1% rule) give you decision-quality information immediately.

Misleading metrics: Gross yield ignores expenses. IRR requires 5-10yr predictions that miss by 15-40%. GRM ignores financing. ROI has no standard definition. None improve deal decisions (Source: NAR, BiggerPockets).

How Do You Calculate Cap Rate for a Rental Property?

Cap rate equals net operating income (NOI) divided by purchase price. NOI is gross rental income minus all operating expenses, excluding the mortgage payment. Cap rate measures the property's return if you paid cash — no financing involved.

Cap Rate Formula: (Gross Annual Rent – Operating Expenses) ÷ Purchase Price × 100

Example: A $300,000 property renting for $2,000/month ($24,000/year):

Table: Cap rate calculation for a $300,000 rental property (Source: NAA, NAR).

Regarding cap rate benchmarks in 2026, the NAA reports average cap rates for US rental properties range from 3.5–5.0% in high-cost markets (Seattle, Boston) to 6.0–8.5% in affordable markets (Columbus, Indianapolis). A cap rate below 4% means the property is priced for appreciation, not cash flow. A cap rate above 8% often signals higher risk — check why the price is low.

Cap rate data: Formula is NOI ÷ purchase price. 2026 averages: 3.5-5.0% high-cost markets, 6.0-8.5% affordable markets. Below 4% = appreciation play. Above 8% = investigate the risk (Source: NAA, NAR).

What Is a Good Cash-on-Cash Return for Rental Property?

Cash-on-cash return (CoC) measures the annual pre-tax cash flow as a percentage of total cash invested. CoC is the most honest metric because it reflects what actually lands in your bank account relative to what you put in.

Cash-on-Cash Formula: Annual Pre-Tax Cash Flow ÷ Total Cash Invested × 100

Example: The same $300,000 property with a $75,000 down payment:

Table: Cash-on-cash calculation showing negative return (Source: NAA, NAR, Freddie Mac).

Regarding this cash-on-cash example, the property loses money — -$8,080 per year on a $75,000 investment. A -10.8% CoC return means the investor pays $8,080 per year for the privilege of owning a property that might appreciate. This is the reality of many US rental properties at 7% mortgage rates.

Good CoC benchmarks for 2026:

• Below 0%: Negative cash flow — the property costs money annually
• 0–5%: Marginal — works only with strong appreciation
• 5–8%: Acceptable — covers costs with modest income
• 8–12%: Strong — real cash flow that compounds
• Above 12%: Excellent — typically found in lower-priced Midwest markets

The BiggerPockets community targets 8% minimum CoC for new acquisitions. Reaching 8% requires either below-market purchase prices, above-average rents, or larger down payments (35%+) that reduce mortgage costs.

CoC data: Formula is annual cash flow ÷ cash invested. Target 8-12% in 2026. Many US properties at 7% rates show negative CoC. 8% minimum is the BiggerPockets standard (Source: BiggerPockets, NAA, Freddie Mac).

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About the Author: PIE Team is the Property Investment Research Team at PIE (Property Intelligence Engine). PIE specialises in AI-driven property market analysis across UK and US markets, combining data science, real estate analytics, and financial modelling. Visit try-pie.com to generate professional AI-powered property investment reports.