Source: https://guthlabs.ai/docs/instruments/rental-property-cash-flow-analyzer/implementation/

instrument implementation / implementation-contract

# Rental Property Cash Flow Analyzer implementation

A source-bound implementation contract for Rental Property Cash Flow Analyzer; deployment and executable qualification remain separate.

Status: **VERIFIED_WITH_ERRATA**Lifecycle: **implementation-contract**

## 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

[01**Overview**](<https://guthlabs.ai/docs/instruments/rental-property-cash-flow-analyzer/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/rental-property-cash-flow-analyzer/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/rental-property-cash-flow-analyzer/qualification/>)

## 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`