Source: https://guthlabs.ai/docs/instruments/pregnancy-due-date-calculator/implementation/

instrument implementation / implementation-contract

# Pregnancy Due Date Calculator implementation

A source-bound implementation contract for Pregnancy Due Date Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**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-clean

**Evidence ID**: t4-242

**Effect**: Computation or source lookup only

## Input and validation requirements

An extreme but valid-at-the-input-boundary JavaScript Date produces a due date beyond the representable Date range and must be rejected or reported as undefined. Additionally, an unlabelled slash-formatted date yields materially different results under MM/DD versus DD/MM conventions.

## 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": {
    "dating_method": "LMP",
    "last_menstrual_period": "2025-01-01",
    "as_of_date": "2025-02-12"
  },
  "expected_outputs": {
    "estimated_due_date": "2025-10-08",
    "gestational_age": "6w0d",
    "trimester": 1
  },
  "working": "Due date: 2025-01-01 + 280 days = 2025-10-08. Gestational age: 2025-02-12 - 2025-01-01 = 42 days. 42 / 7 = 6 weeks with 0 days remaining, so 6w0d. Since 6w0d is before 14w0d, trimester = 1."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/pregnancy-due-date-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/pregnancy-due-date-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/pregnancy-due-date-calculator/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-tranche4/tranche4-results.json`