Usage terms

Updated September 2026

The service

PORTMAN LLC provides RentBuy.org, a free rent-versus-buy calculator available through its website, mobile applications, MCP endpoint and calculator panel in ChatGPT and Claude. It compares hypothetical scenarios using the assumptions supplied by the user and defaults for omitted inputs. It does not arrange mortgages, execute investments, process payments or access financial accounts.

Understanding the model

Results are educational estimates, not personalized financial or tax advice, mortgage offers, or guarantees of future performance. The model uses simplified US tax assumptions and omits the SALT cap, mortgage-interest limit, PMI and capital-gains taxes. The comparison covers 30 years. Yearly net worth is before selling costs; the headline includes selling costs at year 30.

Both households invest housing savings at the same assumed return. Investment returns, appreciation, rent growth and expenses can differ from your assumptions. Monte Carlo results describe sensitivity to assumptions and are not market forecasts. Review the full inputs and limitations before using a result in your own planning.

Using the calculator

Use the service for scenario analysis. Do not submit account credentials or bank account information. Do not attempt to disrupt the service or circumvent its request limits.

Privacy and availability

The privacy policy describes local input storage, MCP request processing and data sharing in ChatGPT and Claude. Features and calculations may be updated, and the service may be temporarily unavailable.

Contact

For questions about these terms or the service, contact admin@rentbuy.org or visit Support.