APR vs APY Converter 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

t4-008

Effect

Computation or source lookup only

Input and validation requirements

The n=0 input creates division by zero and an undefined exponentiation, so the converter must reject it rather than return a numeric APY. The unit-ambiguity vector also shows that accepting an unlabeled APR value can produce materially different results.

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": {
    "direction": "APR_to_APY",
    "APR": 0.12,
    "n": 12
  },
  "expected_outputs": {
    "APY": 0.12682503013196977,
    "difference_APY_minus_APR": 0.00682503013196977
  },
  "working": "APR/n = 0.12/12 = 0.01. APY = (1+0.01)^12 - 1 = 1.01^12 - 1 = 1.1268250301319698 - 1 = 0.12682503013196977. Difference = APY - APR = 0.12682503013196977 - 0.12 = 0.00682503013196977."
}

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