Ordinary Annuity FV/PV 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-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

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