Calculation Methodology.
The exact formulas, conventions and limits behind every figure on this site.
Last materially reviewed: July 2026 · Maintained by the Stonehaven team · Corrections: office@stonehavencre.com
Deterministic code, not estimates by judgment
Every number our calculators display is produced by deterministic, unit-tested code. No figure is generated by an AI model, adjusted editorially, or fitted to a marketing narrative. The same functions that render on-page results are exercised by automated fixtures with independently verified expected values before any change ships.
The residential DSCR convention we model
For 1-4 unit rental properties we model the common industry convention: DSCR = eligible monthly rent ÷ monthly PITIA, where PITIA is principal and interest plus one-twelfth of annual property taxes and insurance plus monthly association dues. Principal and interest uses the standard amortization formula at the entered rate and term; interest-only scenarios use loan × monthly rate. A zero-rate edge case amortizes straight-line. Lenders vary in how they treat rent evidence, expenses and minimum ratios - our output models the entered assumptions, not any specific program.
Investor cash flow is deliberately different
The investor view subtracts vacancy from rent, then management (on collected rent), maintenance and capital-expenditure reserves (on gross rent), plus taxes, insurance and dues, to reach estimated NOI; investor DSCR divides NOI by principal-and-interest debt service. This is intentionally more conservative than the lender formula, and the two are never mixed.
Target-ratio sizing
Rent needed at a target ratio is PITIA × target. Maximum supportable housing expense is rent ÷ target; maximum principal and interest subtracts taxes, insurance and dues from that figure before any loan amount is derived; the illustrative maximum loan inverts the amortization formula at the entered rate and term. Sizing figures are illustrative mathematics, not program limits.
What these calculators do not determine
Eligibility, approval, pricing, leverage limits, reserve requirements, rent-evidence treatment, property eligibility or closing timelines. Those are determined by the selected third-party lender through underwriting. Stonehaven arranges financing and performs preliminary analysis; the selected lender makes the credit decision.
Prepayment explainer
The prepayment module multiplies the entered balance by the step percentage of an illustrative structure for the chosen exit year. Structures vary by lender and state, and some states restrict certain penalties; final loan documents control.