Docs · Model reference

having-a-child

Verified · spec v1.0.0

Full specification JSON contract Live demo calculator

Inputs

Field	Type	Valid domain
annualIncome	float	40,000 – 500,000
currentSavingsRate	float	0.01 – 0.5
currentSavings	float	0 – 1,000,000
currentAge	int	22 – 60
retirementAge	int	45 – 75
annualReturn	float	0.02 – 0.15
marginalTaxRate	float	0.1 – 0.5
firstYearCost	float	5,000 – 50,000
ongoingAnnualCost	float	3,000 – 40,000
childcareYears	int	0 – 10
childcareAnnualCost	float	0 – 50,000
college529Monthly	float	0 – 1,000

retirementAge must exceed currentAge

All fields required. Out-of-domain values are rejected with per-field errors — never clamped. Unknown fields are rejected.

Live example — generated from the real engine

Request

POST /api/v1/models/having-a-child
{
  "annualIncome": 270000,
  "currentSavingsRate": 0.26,
  "currentSavings": 500000,
  "currentAge": 41,
  "retirementAge": 60,
  "annualReturn": 0.09,
  "marginalTaxRate": 0.3,
  "firstYearCost": 28000,
  "ongoingAnnualCost": 22000,
  "childcareYears": 5,
  "childcareAnnualCost": 25000,
  "college529Monthly": 500
}

Response (chart arrays compacted)

{
  "ok": true,
  "model": "having-a-child",
  "specVersion": "1.0.0",
  "contractUrl": "/api/v1/models/having-a-child",
  "specUrl": "/api/v1/models/having-a-child/spec",
  "inputs": {
    "annualIncome": 270000,
    "currentSavingsRate": 0.26,
    "currentSavings": 500000,
    "currentAge": 41,
    "retirementAge": 60,
    "annualReturn": 0.09,
    "marginalTaxRate": 0.3,
    "firstYearCost": 28000,
    "ongoingAnnualCost": 22000,
    "childcareYears": 5,
    "childcareAnnualCost": 25000,
    "college529Monthly": 500
  },
  "outputs": {
    "totalFirstYearCost": 28000,
    "totalChildCostToAdulthood": 439000,
    "savingsRateImpact": 2532.4074074074074,
    "fireImpactYears": 3.4166666666666665,
    "retirementWealthWithChild": 3714835.0017737933,
    "retirementWealthWithout": 5200510.200275814,
    "college529At18": 268175.83702424646,
    "yearlyData": [
      {
        "year": 41,
        "withChild": 500000,
        "withoutChild": 500000
      },
      {
        "year": 42,
        "withChild": 563751.1111111111,
        "withoutChild": 594140
      },
      "… 18 more"
    ]
  },
  "sentinels": [],
  "assumptions": [
    "Implements model spec having-a-child v1.0.0 (dual-implementation verified).",
    "retirementAge must exceed currentAge"
  ],
  "facts": [],
  "record": {
    "sha256": "da6d7fc3e8c20d94c66fc319e51663acd25347151dba97b19922b2615cd9355a",
    "fields": [
      "model",
      "specVersion",
      "inputs",
      "outputs"
    ],
    "howToVerify": "Store this record with any advice or agent output built on these numbers. To verify later: build {model, specVersion, inputs, outputs} from the stored response, serialize as JSON with object keys sorted recursively (no whitespace), and SHA-256 it — a match proves the numbers came from this spec version with these inputs, unaltered."
  },
  "disclaimer": "Illustrative planning model, not financial advice. Outputs follow the published model spec exactly; read the spec for assumptions and exclusions before relying on any number."
}

This example is executed against the production engine when the page builds — it cannot drift from the API's real behavior.