Pregnancy due date (Naegele's rule) API

Compute the estimated due date and current gestational age via Naegele's rule (LMP + 280 days, cycle-adjusted), with trimester and an estimated conception date. Answers 'when is my due date', 'how many weeks pregnant am I', 'due date from last period', 'Naegele due date calculator'.

Price$0.01per request

MethodPOST

Route/v1/health/due-date

StatusLive

MIME typeapplication/json

Rate limit120/minute

CacheNo cache

healthdue-datepregnancynaegelegestationlmpobstetricscalculator

API URLhttps://x402.hexl.dev/v1/health/due-date

Integration docs

Example request

{
  "lmpDate": "2025-01-01",
  "asOfDate": "2025-04-01"
}

Example response

{
  "dueDate": "2025-10-08",
  "method": "Naegele's rule (LMP + 280 days, cycle-adjusted)",
  "conceptionDateEst": "2025-01-15",
  "gestationalAge": {
    "weeks": 12,
    "days": 6,
    "totalDays": 90
  },
  "trimester": "first",
  "inputs": {
    "lmpDate": "2025-01-01",
    "cycleLength": 28,
    "asOfDate": "2025-04-01"
  }
}

Input schema

{
  "type": "object",
  "required": [
    "lmpDate"
  ],
  "properties": {
    "lmpDate": {
      "type": "string",
      "description": "First day of last menstrual period (ISO date)",
      "examples": [
        "2025-01-01"
      ]
    },
    "cycleLength": {
      "type": "number",
      "default": 28,
      "examples": [
        28
      ]
    },
    "asOfDate": {
      "type": "string",
      "description": "Reference date for gestational age (ISO)",
      "examples": [
        "2025-04-01"
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}