Source: https://guthlabs.ai/docs/instruments/ordinary-annuity-fv-pv/implementation/

instrument implementation / implementation-contract

# Ordinary Annuity FV/PV implementation

A source-bound implementation contract for Ordinary Annuity FV/PV; 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**: t2-020

**Effect**: Computation or source lookup only

## Input and validation requirements

The formulas require domain and convention handling that is not explicit: zero-rate handling needs a limiting implementation, r=-1 makes PV undefined, and an unlabelled rate value such as 5 produces radically different results depending on whether it means 5% or decimal 5.

## 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": {
    "PMT": 1000,
    "rate_per_period": 0.05,
    "n": 3,
    "timing": "ordinary"
  },
  "expected_outputs": {
    "FV": 3152.5,
    "PV": 2723.248029,
    "total_contributions": 3000,
    "FV_growth": 152.5
  },
  "working": "FV=1000*((1.05)^3-1)/0.05=1000*(1.157625-1)/0.05=1000*0.157625/0.05=3152.50. PV=1000*(1-(1.05)^(-3))/0.05=1000*(1-0.8638375985)/0.05=1000*0.1361624015/0.05=2723.248029. Total contributions=1000*3=3000. FV growth=3152.50-3000=152.50."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/ordinary-annuity-fv-pv/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/ordinary-annuity-fv-pv/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/ordinary-annuity-fv-pv/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-tranche2/tranche2-results.json`