Source: https://guthlabs.ai/docs/instruments/bond-price-ytm-calculator/implementation/

instrument implementation / implementation-contract

# Bond Price / YTM Calculator implementation

A source-bound implementation contract for Bond Price / YTM Calculator; 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**: t6-031

**Effect**: Computation or source lookup only

## Input and validation requirements

The instrument has a mathematically undefined input at market_yield = -1 and should reject it. Separately, the unspecified coupon and yield frequency creates materially different valid prices under annual versus semiannual conventions.

## 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": {
    "mode": "price",
    "face_value": 1000,
    "coupon_rate": 0.05,
    "years_to_maturity": 5,
    "annual_coupon_frequency": 1,
    "market_yield": 0.04
  },
  "expected_outputs": {
    "price": 1044.518223,
    "current_yield": 0.047868959
  },
  "working": "C = 1000 × 0.05 = 50. Price = 50/(1.04)^1 + 50/(1.04)^2 + 50/(1.04)^3 + 50/(1.04)^4 + 50/(1.04)^5 + 1000/(1.04)^5. (1.04)^5 = 1.2166529024, so 1/(1.04)^5 = 0.8219271068. Coupon annuity factor = (1 - 0.8219271068)/0.04 = 4.451822330. Coupon PV = 50 × 4.451822330 = 222.5911165. Principal PV = 1000 × 0.8219271068 = 821.9271068. Price = 222.5911165 + 821.9271068 = 1044.5182233. Current yield = 50/1044.5182233 = 0.047868959, or 4.7868959%."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/bond-price-ytm-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/bond-price-ytm-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/bond-price-ytm-calculator/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-tranche6/tranche6-results.json`