Rental property calculator
Get cap rate, cash flow, and cash-on-cash return on any rental in seconds, with real county-level property tax for 3,100+ US counties from Census data, not a national average that quietly breaks the verdict in high-tax markets. Honest, deterministic math. No signup.
Pick a county to use its real effective property-tax rate, from Census data for 3,100+ US counties. Insurance stays a per-state estimate.
Every number is editable. Defaults match the Mortar extension: 20% down, 7.5% for 30 years, 8% vacancy, 10% maintenance, 10% management.
- Rent$2,200
- Property tax state avg, 1.80%-$525
- Insurance state avg, 1.05%-$306
- Vacancy 8% of rent-$176
- Maintenance 10% of rent-$220
- Management 10% of rent-$220
- Net operating income$753/mo
- Mortgage P&I 20% down at 7.5%, 30 yr-$1,958
- Cash flow-$1,205/mo
- Cash invested 20% down$70,000
Typing a dozen numbers per listing gets old. The Mortar Chrome extension reads them off any Zillow page, adds a rent estimate, and shows this same math in one click.
Estimates only. Verify rent comps, taxes and condition before making an offer. This is not financial advice or an appraisal.
Screening a lot of listings?
The Mortar Chrome extension runs this exact analysis automatically on any Zillow, Redfin, Realtor.com, or Homes.com listing, no typing. Free to start.
How to read these numbers
Cap rate is the property's annual net operating income divided by its price, ignoring financing. It's the cleanest way to compare two properties on equal footing because it strips out your particular loan.
Cash-on-cash return is your annual pre-tax cash flow divided by the cash you put in (here, the down payment). It answers "what is my actual return on the money I invested?" and changes with your down payment and interest rate.
Monthly cash flow is what lands in your pocket after the mortgage and every operating expense: property tax at your county's real rate, insurance, HOA dues, plus reserves for vacancy, maintenance and management (8% / 10% / 10% by default, all adjustable). A deal that looks great on price can still bleed every month once real local taxes are in.
Frequently asked questions
How do you calculate cap rate on a rental property?
Cap rate is annual net operating income (rent minus operating expenses, before mortgage) divided by the purchase price. This calculator computes it deterministically from your inputs plus real per-state property tax and insurance, then shows the result as a percentage.
What is a good cap rate or cash-on-cash return?
It depends on your market and strategy, but many buy-and-hold investors look for a cap rate above 7% and cash-on-cash above 8% with positive monthly cash flow. This tool flags those thresholds as a starting point, not a recommendation. Always verify against local comps.
Why does the county matter for a rental analysis?
Property tax varies enormously by location, and often as much within a state as between states. A flat national average (around 1.2% tax) makes deals in high-tax markets like Texas, Illinois and New Jersey look far better than they really are, and even a state average can miss your county by half a percent of the purchase price every year. Pick your county and this calculator uses its real effective rate; leave it on statewide average and you get the same per-state rate the rest of Mortar uses.
Where do the county property tax rates come from?
US Census Bureau American Community Survey data: each county's aggregate real estate taxes paid divided by aggregate home value, covering 3,100+ counties, calibrated to the same per-state baselines used across Mortar. They estimate the county's typical effective rate. Your parcel's actual assessment can differ, so verify before you offer.
Is this the same as the Mortar Chrome extension?
It uses the same deterministic math. The free calculator is for running numbers by hand; the Mortar Chrome extension does it automatically on any Zillow listing: it reads the price and details off the page, resolves the county's tax rate on its own, adds a rent estimate, and analyzes the deal in about ten seconds.
Are these numbers financial advice?
No. Every figure is an estimate to help you screen deals quickly. It is not financial, investment or real-estate advice, and it is not an appraisal. Verify rent comps, taxes and condition before making an offer.
Prefer the full write-up? Read the Mortar blog on analyzing rentals.
More free calculators
Net operating income over price, computed with real per-state property tax and insurance.
What the cash you actually put in earns, with your own down payment, rate and term.
Monthly rent minus mortgage and every honest expense line, including reserves.
Work backwards: the highest price at which a deal still clears your cash flow and return targets.
Prefer the full write-up? Read the Mortar blog on analyzing rentals.