Source: https://guthlabs.ai/docs/instruments/apr-vs-apy-converter/implementation/

instrument implementation / implementation-contract

# APR vs APY Converter implementation

A source-bound implementation contract for APR vs APY Converter; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**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-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

[01**Overview**](<https://guthlabs.ai/docs/instruments/apr-vs-apy-converter/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/apr-vs-apy-converter/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/apr-vs-apy-converter/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-tranche4/tranche4-results.json`