Data sources & methodology

RentDealBase runs entirely in your browser. You enter purchase price, rents, expenses, and loan assumptions — we apply documented underwriting arithmetic. This page lists the core formulas and the limits. Nothing here is an appraisal, loan offer, or tax advice.

Core formulas

• EGI / NOI: Vacancy loss = GPR × vacancy%; EGI = GPR − vacancy + other income; NOI = EGI − operating expenses (not debt).
• Cap rate: Cap% = NOI ÷ Purchase price.
• Cash flow / CoC: Annual CF = NOI − annual debt service; CoC% = Annual CF ÷ Cash invested.
• Debt service: Standard amortizing PI from principal, annual rate, and term (months). Optional interest-only on the payment tool.
• DSCR: DSCR = NOI ÷ annual debt service.
• Rules of thumb: 1%/2% = monthly rent ÷ price; 50% rule OpEx ≈ 0.5 × gross rent (before mortgage).

What we do not pull

• No address API, Zillow rent estimate, or AVM
• No lender rate lock, credit check, or loan application
• No tax / depreciation schedule — income-tax results are yours or your CPA's
• No MLS comps scrape — ARV tools use comps you paste

Known simplifications

• Default PI excludes escrowed taxes and insurance unless you add them to OpEx or debt
• Year-one cash flow is not a 10-year IRR or equity multiple
• Rule-of-thumb screens are filters, not buy signals
• STR tools use ADR × occupancy — not an Airbnb/Vrbo connection

Corrections

Found a wrong formula? Email contact@rentdealbase.com with the page URL and inputs. Also see About and all calculators.