Rental Property Cash Flow Analyzer implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-with-binding-errata

Evidence ID

t5-166

Effect

Computation or source lookup only

Input and validation requirements

The extreme input overflows JavaScript arithmetic, and the zero-expense boundary makes expense-pie percentages undefined. The specification also lacks a stated branch or validation rule for percentages above 100% and does not clarify whether percentage inputs use percent points or decimal fractions.

Required corrections

[
  {
    "vector": 2,
    "field": "monthly/annual_net_cash_flow",
    "wrong": "347 / 4164",
    "correct": "383 / 4596",
    "cause": "outputs contradict own working, which computes AND self-corrects to 383"
  }
]

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "rent": 2400,
    "mortgage_payment": 1200,
    "taxes": 200,
    "insurance": 100,
    "HOA": 50,
    "vacancy_pct": 0.05,
    "maintenance_pct": 0.08,
    "mgmt_fee_pct": 0.1
  },
  "expected_outputs": {
    "monthly_net_cash_flow": 298,
    "annual_net_cash_flow": 3576,
    "expense_breakdown": {
      "mortgage": 1200,
      "taxes": 200,
      "insurance": 100,
      "HOA": 50,
      "vacancy": 120,
      "maintenance": 192,
      "property_management": 240,
      "total_expenses": 2102
    }
  },
  "working": "Vacancy = 2400*0.05 = 120. Maintenance = 2400*0.08 = 192. Management = 2400*0.10 = 240. Total expenses = 1200+200+100+50+120+192+240 = 2102. Monthly cash flow = 2400-2102 = 298. Annual cash flow = 298*12 = 3576."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche5/tranche5-results.json
• tranche errata record