Source: https://guthlabs.ai/docs/instruments/amortization-schedule/implementation/

instrument implementation / implementation-contract

# Amortization Schedule implementation

A source-bound implementation contract for Amortization Schedule; deployment and executable qualification remain separate.

Status: **VERIFIED_WITH_ERRATA**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-with-binding-errata

**Evidence ID**: t3-008

**Effect**: Computation or source lookup only

## Input and validation requirements

A term of zero makes the payment calculation divide by zero and must be rejected. The specification also omits payment frequency and rate convention, so identical-looking rate and term inputs can produce materially different schedules.

## 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": {
    "principal": 1200,
    "annual_rate": 0,
    "payment_frequency": "monthly",
    "term_periods": 3,
    "extra_payment": 0,
    "rounding": "nearest cent"
  },
  "expected_outputs": {
    "table": [
      {
        "period": 1,
        "interest": 0,
        "principal": 400,
        "balance": 800
      },
      {
        "period": 2,
        "interest": 0,
        "principal": 400,
        "balance": 400
      },
      {
        "period": 3,
        "interest": 0,
        "principal": 400,
        "balance": 0
      }
    ],
    "payoff_period": 3,
    "payoff_date": null
  },
  "working": "Monthly rate r=0.00/12=0.00. PMT=P/n=1200.00/3=400.00. Period 1: interest=1200.00*0.00=0.00; principal=400.00-0.00=400.00; balance=1200.00-400.00=800.00. Period 2: interest=800.00*0.00=0.00; principal=400.00; balance=800.00-400.00=400.00. Period 3: interest=400.00*0.00=0.00; principal=400.00; balance=400.00-400.00=0.00."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/amortization-schedule/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/amortization-schedule/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/amortization-schedule/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-tranche3/tranche3-results.json`