Online Tool Store
· 4 min read
How to Calculate a Rental Property's Cap Rate
Heshan Fernando
Co-founder & COO
You’re comparing two rental properties — one priced higher with more rental income, one cheaper with lower income — and trying to figure out which is actually the better deal on a like-for-like basis. Price alone doesn’t answer that, and neither does rental income alone; a $500,000 property bringing in $40,000 a year isn’t automatically better or worse than a $300,000 property bringing in $27,000 without a way to normalize for the price difference.
That’s exactly what cap rate is for. It’s one of the most commonly cited numbers in real estate investing precisely because it lets you compare deals of very different sizes on the same footing.
What cap rate actually measures
Capitalization rate is a property’s net operating income divided by its current value or purchase price, expressed as a percentage. Net operating income means rental income minus operating expenses — property taxes, insurance, maintenance, management fees — but before mortgage payments, since cap rate is meant to measure the property’s return independent of how it’s financed.
A higher cap rate generally suggests a better return relative to the property’s price, but it isn’t automatically “better” in isolation — cap rates vary meaningfully by location, property type, and risk profile, so a very high cap rate in a declining market isn’t necessarily a better deal than a lower cap rate in a stable, appreciating one.
Why people get stuck here
- Confusing gross income with net operating income. Using rental income before subtracting operating expenses inflates the cap rate and misrepresents the property’s actual return.
- Including mortgage payments by mistake. Cap rate is meant to be financing-independent, so debt service shouldn’t factor into the calculation — that’s a separate metric (cash-on-cash return) entirely.
- Comparing cap rates across very different markets. A 6% cap rate means something different in a stable, expensive metro area than it does in a higher-risk, lower-cost one — the number alone doesn’t capture that context.
- Using outdated or optimistic expense estimates. Underestimating maintenance, vacancy, or management costs artificially inflates the calculated cap rate compared to what you’ll actually experience.
What a good cap rate calculator looks like
Clear separation of income and expenses
The tool should walk through rental income and operating expenses as distinct inputs, rather than asking for a single pre-calculated “net income” figure that hides how it was derived.
Excludes financing from the calculation
Since cap rate is meant to be independent of how the deal is financed, mortgage payments and interest shouldn’t be part of the inputs at all.
Makes it easy to compare multiple properties
Because the whole point of cap rate is comparing deals against each other, being able to quickly re-run the numbers for a second or third property matters as much as getting one number right.
Common mistakes to avoid
- Using gross rental income instead of net operating income, which overstates the actual cap rate.
- Including mortgage payments in the expense side of the calculation, which conflates cap rate with a financing-dependent metric.
- Comparing a cap rate from one market directly against a cap rate from a very different market without accounting for the risk and growth differences behind the numbers.
- Using unrealistically low expense estimates, especially for maintenance and vacancy, which makes a property look more attractive than it will actually perform.
- Treating cap rate as the only metric that matters — it’s one useful comparison tool, not a complete investment analysis on its own.
How to do it with Cap Rate Calculator
Online Tool Store’s Cap Rate Calculator runs entirely in your browser and walks through income, expenses, and property value separately.
- Enter the property’s rental income.
- Enter its operating expenses — taxes, insurance, maintenance, and management, but not mortgage payments.
- Enter the property’s value or purchase price.
- Get the calculated cap rate, ready to compare against other properties you’re evaluating.
Because it’s quick to re-run, you can compare several properties side by side in the same sitting instead of doing each calculation separately by hand.
Frequently asked questions
What’s considered a “good” cap rate?
It depends heavily on the market and property type — cap rates in expensive, stable metro areas tend to run lower, while higher-risk or lower-cost markets tend to run higher. There’s no universal good number; it’s a comparative tool, not an absolute grade.
Does cap rate account for my mortgage payment?
No — cap rate is deliberately calculated before financing costs, so it reflects the property’s return independent of how you’re paying for it. If you want a return figure that accounts for your specific financing, that’s a different metric, cash-on-cash return.
Can cap rate go negative?
Yes, if operating expenses exceed rental income, producing a negative net operating income and therefore a negative cap rate — a clear signal the property isn’t generating a positive return from operations alone, regardless of price appreciation potential.
Final thought
Cap rate is a fast way to compare rental properties on equal footing, but it’s a snapshot of operating performance, not a full investment analysis on its own. Use it to narrow down candidates, then dig into the specifics before making an offer.