What cap rate actually means — and where the metric breaks

The formula

Cap rate is the unlevered annual return: the percentage an investor would earn buying the property all-cash, ignoring appreciation. NOI is gross potential rent minus vacancy minus operating expenses; it excludes debt service, depreciation, capital expenditures, and income taxes. The clean version:

Cap Rate = NOI / Property Value

Direct-cap valuation reverse:
  Property Value = NOI / Cap Rate

Where it works

Cap rate is at its most useful when comparing comparable stabilized income properties at scale — say, three competing 150-unit class-B garden apartments in the same submarket. The metric strips out the financing decision (cap rate is unlevered) and the buyer-specific tax position (NOI is pre-tax, pre-depreciation), giving a cleaner apples-to-apples comparison than IRR or cash-on-cash would.

NCREIF Property Index publishes quarterly cap-rate benchmarks by sector and region — a defensible reference for whether a specific market's pricing is in-line, compressed, or dislocated relative to long-run averages.

Where it breaks: small deals

On a single-family rental or 2-4 unit small multifamily, NOI is dominated by repair-and-maintenance volatility. One $5,000 furnace replacement can swing a year's NOI by 10–20%, which means the "cap rate" on that property is essentially a noise figure. Cash-on-cash and 5-year IRR are more useful for these deals because they integrate the financing decision (which is the whole point of doing small deals — you can't do them all-cash and earn back your time).

Where it breaks: pre-stabilization deals

On a heavy-value-add or pre-stabilization property, current NOI is below stabilized NOI by definition. Using current NOI to compute cap rate gives an artificially low number that doesn't reflect post-rehab economics. The fix: stabilized-NOI / total-project-cost (sometimes called "yield on cost"). The math is honest, but watch for the next trap — operators inflate stabilized rent assumptions, so the yield-on-cost number is only as defensible as the underwriter's rent-comp methodology.

Where it breaks: cap-rate compression cycles

A static cap rate ignores the future rent trajectory. In a fast-growing market — say, 5% annual rent growth — a 4% cap rate today implies a defensible 8%+ IRR over a 10-year hold. In a flat-rent market, that same 4% cap rate is a 4% IRR. Cap-rate compression cycles end when the rent-growth assumption decompresses, which usually arrives in waves: rates rise, equity required-return rises, weighted-average required cap rate rises, prices fall.

The Gordon-growth-model relationship: cap rate ≈ discount rate − growth rate. When growth assumptions reset down or discount rate resets up, cap rates expand. 2022 was an example.

The band-of-investment derivation

A useful sanity check: derive a "fair" cap rate from underlying debt and equity returns, weighted by their share of the capital stack:

Cap Rate = (LTV × Mortgage Constant) + ((1 − LTV) × Equity Yield)

  Mortgage Constant = annual debt service / loan amount
  Equity Yield = target cash-on-cash return (typical 8–10%)

Example: 70% LTV at 7% interest, 25-year amortization
  Mortgage constant ≈ 8.5%
  Equity yield target = 9%
  Cap Rate = (0.70 × 0.085) + (0.30 × 0.09)
           = 5.95% + 2.70%
           = 8.65%

When market cap rates trade well below the band-of-investment number, prices are anticipating rent growth or rate falls. When they trade above, the market is pricing in distress or financing dysfunction. The framework doesn't tell you which is right — but it gives you a benchmark for whether the market has priced in something specific you should question.

Run the numbers yourself

The Cap Rate Calculator computes cap rate from NOI inputs, runs the band-of-investment derivation, and reverses to a direct-cap valuation given a target cap rate. It also includes the sensitivity table on vacancy and operating-expense assumptions — because the gap between "listing pro-forma cap" and "underwritten cap" is often 100–200 basis points and the only way to see the gap is to put both numbers next to each other.

Sources

• Damodaran NYU Stern — sector cost of capital, real-estate equity risk premiums
• NCREIF Property Index — quarterly cap-rate benchmarks
• Fannie Mae Selling Guide §B6 — multifamily underwriting + DSCR thresholds
• Income property methodology — full primary-source treatment