Effective Annual Rate Comparator (Multiple Loans/Cards) 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

t5-229

Effect

Computation or source lookup only

Input and validation requirements

A zero-principal offer makes fee amortization undefined, so the instrument must reject it. The specification also leaves fee sign and fee-amortization basis ambiguous, producing materially different effective costs.

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": {
    "offers": [
      {
        "id": "A",
        "principal": 10000,
        "nominal_annual_rate": 0.12,
        "origination_fee": 0,
        "term_years": 1,
        "compounding_periods_per_year": 12
      },
      {
        "id": "B",
        "principal": 10000,
        "nominal_annual_rate": 0.118,
        "origination_fee": 0,
        "term_years": 1,
        "compounding_periods_per_year": 4
      }
    ]
  },
  "expected_outputs": {
    "ranked_by_ear": [
      "B",
      "A"
    ],
    "offers": {
      "A": {
        "ear": 0.12682503
      },
      "B": {
        "ear": 0.123324947
      }
    }
  },
  "working": "A: (1+0.12/12)^12-1 = (1.01)^12-1 = 1.126825030-1 = 0.126825030, or 12.682503%. B: (1+0.118/4)^4-1 = (1.0295)^4-1 = 1.123324947-1 = 0.123324947, or 12.332495%. Therefore B ranks below A."
}

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