About ROI Math

Our mission

Good underwriting math should not require a paid subscription or a messy spreadsheet. ROI Math exists to make the core return calculations every property investor relies on fast, free, and easy to trust — with the formulas shown in plain sight so you can check the work.

Who is behind ROI Math

ROI Math is an independent project built and maintained by a solo developer and real estate investor based in North America, with more than 10 years of hands-on buy-and-hold rental experience. The calculators reflect the same underwriting math used to evaluate real deals over that decade. ROI Math is not backed by a brokerage, lender, or data vendor, so the tools stay focused on one thing: clear, unbiased investment math.

How our calculators work

Every calculator runs entirely in your browser and updates as you type — nothing you enter is sent to a server. The formulas are standard, widely used real estate metrics:

• Cap rate = net operating income ÷ purchase price. Try the cap rate calculator.
• Cash-on-cash return = annual pre-tax cash flow ÷ cash invested. Try the cash-on-cash return calculator.
• Mortgage payment = amortized principal and interest plus optional taxes, insurance, and HOA. Try the mortgage calculator.
• DSCR = net operating income ÷ annual debt service. Try the DSCR calculator.
• GRM = purchase price ÷ annual gross income. Try the GRM calculator.
• Break-even occupancy = required rent revenue ÷ gross scheduled rent. Try the break-even occupancy calculator.
• Property tax = home value × effective tax rate. Try the property tax calculator.

Where our data comes from

The property tax tools use 2020–2024 ACS 5-year estimates from the U.S. Census Bureau. State benchmarks are calculated as aggregate real estate taxes paid (table B25090) divided by aggregate owner-occupied home value (table B25082). These figures cover owner-occupied housing, so rental and commercial property can be classified or taxed differently. Real bills also depend on county, city, school district, assessment, and exemption rules. Use the result for education and comparison, then confirm the parcel with the local assessor before budgeting or closing.

What we stand for

• Free to use, with no account or sign-up required.
• No analytics, no tracking cookies, and no selling of your data — see our privacy policy.
• Transparent formulas you can verify yourself.
• Educational estimates, never financial or tax advice.

Get in touch

Found an error, have a feature request, or want a calculator for your state? Email hello@roimath.com or visit the contact page.