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.
- Property tax = home value × effective tax rate. Try the property tax calculator.
Where our data comes from
The property tax tools use each state's approximate average effective property tax rate (annual tax paid divided by home value) to produce a quick estimate. Real tax bills depend on county, city, and school district rates plus exemptions, so these figures are for education and comparison, not for closing or budgeting. Always confirm specifics with your local assessor and your own professional advisors.
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.
Last updated 2026-05-31.