Retirement Nest Egg (4% Rule) Estimator 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-clean

Evidence ID

t5-204

Effect

Computation or source lookup only

Input and validation requirements

• target_nestegg causes division by zero when withdrawal_rate is 0%; reject zero before calculation.
• Negative withdrawal rates, negative balances, or negative annual spending should be rejected as invalid inputs.
• Very small positive withdrawal rates can produce extremely large target nest-egg values and may require range or overflow handling.
• Rates above 100% are mathematically computable but generally require an explicit warning or validation rule.
• The 4% rule is a historical rule of thumb, not a guaranteed sustainable withdrawal rate; the stated honest label should be displayed prominently and the result must not be presented as individualized financial advice.

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": {
    "calculation": "sustainable_withdrawal",
    "balance": 1000000,
    "withdrawal_rate_percent": 4
  },
  "expected_outputs": {
    "sustainable_annual_withdrawal": 40000
  },
  "working": "Convert 4% to decimal: 4 ÷ 100 = 0.04; multiply balance by rate: 1,000,000 × 0.04 = 40,000."
}

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-tranche5/tranche5-results.json