PMI / LTV Estimator 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-clean

Evidence ID

t4-032

Effect

Computation or source lookup only

Input and validation requirements

The specification has a division-by-zero failure when home_value is zero and cannot compute a payment count for any ordinary case because it provides no payment amount, principal-per-payment value, interest rate, or amortization schedule. The PMI-rate input also has a potentially severe percent-versus-decimal convention ambiguity.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

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

{
  "inputs": {
    "loan_balance": 360000,
    "appraised_value": 450000,
    "pmi_rate_percent": 0.5,
    "principal_reduction_per_payment": 1500
  },
  "expected_outputs": {
    "ltv_percent": 80,
    "estimated_pmi_cost_per_year": 1800,
    "estimated_payments_to_80_ltv": 0
  },
  "working": "LTV = 360000 ÷ 450000 × 100 = 0.8 × 100 = 80%. PMI rate = 0.5 ÷ 100 = 0.005. Annual PMI = 360000 × 0.005 = 1800. 80% target balance = 450000 × 0.80 = 360000. Balance gap = 360000 − 360000 = 0. Payments = max(0, 0 ÷ 1500) = 0."
}

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-tranche4/tranche4-results.json