Car Loan / Total Cost of Ownership Calculator 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

t5-220

Effect

Computation or source lookup only

Input and validation requirements

A zero-month term creates a zero amortization denominator and produces an undefined payment; the calculator should reject nonpositive terms. The specification also leaves the resale-percentage basis ambiguous, which can change TCO materially.

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": {
    "price": 30000,
    "down_payment": 5000,
    "apr": 0,
    "term_years": 5,
    "ownership_years": 5,
    "annual_insurance": 1800,
    "annual_fuel": 2400,
    "annual_maintenance": 900,
    "resale_percentage": 0.4
  },
  "expected_outputs": {
    "monthly_payment": 416.67,
    "total_interest": 0,
    "resale_value": 12000,
    "full_tco": 38500
  },
  "working": "P=30000−5000=25000. N=5×12=60. Because r=0, M=P/N=25000/60=416.6667, displayed as 416.67. Total interest=M×N−P=25000−25000=0. Annual ownership costs=1800+2400+900=5100. Five-year ownership costs=5100×5=25500. Resale value=30000×0.40=12000. Full TCO=25000+25500−12000=38500."
}

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