# Pregnancy Due Date API > Pregnancy and due-date maths as an API, using the standard Naegele's rule (40 weeks / 280 days from the last menstrual period). The due-date endpoint takes the last menstrual period, the conception date, or a known due date — whichever you have — and returns the due date, the estimated conception date and the fertile window. The gestational-age endpoint reports how far along a pregnancy is as of any reference date: gestational age in weeks and days, the trimester, days remaining, progress percent, and whether it is overdue. The milestones endpoint lists the key dates of a pregnancy — the trimester boundaries, the anatomy-scan window, viability at 24 weeks, full term at 37–40 weeks, the due date and post-term at 42 weeks. All dates are handled in UTC and computed locally and deterministically. Ideal for pregnancy and fertility apps, midwifery and clinical tools, and parenting and family-planning products. Informational only — not medical advice. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 4 endpoints. This is pregnancy date maths; for general date arithmetic use a datetime API. ## Authentication All requests require your oanor API key in the `x-oanor-key` header. Get one at https://www.oanor.com/developer/keys. ```bash curl -H "x-oanor-key: oanor_live_…" "https://api.oanor.com/pregnancy-api/..." ``` ## Pricing - **Free** (Free) — 7,035 calls/Mo, 2 req/s - **Starter** ($9/Mo) — 16,550 calls/Mo, 8 req/s - **Pro** ($28/Mo) — 216,500 calls/Mo, 20 req/s - **Mega** ($66/Mo) — 1,125,000 calls/Mo, 50 req/s ## Endpoints ### Pregnancy #### `GET /v1/due-date` — Due date from LMP / conception / due **Parameters:** - `lmp` (query, optional, string) — Last menstrual period YYYY-MM-DD Example: `2025-01-01` - `conception` (query, optional, string) — Or conception date - `due_date` (query, optional, string) — Or a known due date **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/pregnancy-api/v1/due-date?lmp=2025-01-01" ``` **Response:** ```json { "data": { "lmp": "2025-01-01", "basis": "last menstrual period", "due_date": "2025-10-08", "fertile_window": { "end": "2025-01-16", "start": "2025-01-10" }, "estimated_conception": "2025-01-15" }, "meta": { "timestamp": "2026-06-03T17:42:10.473Z", "request_id": "a3df4855-198f-436f-b9ec-e49175cb6a26" }, "status": "ok", "message": "Due date", "success": true } ``` #### `GET /v1/gestational-age` — Gestational age + progress **Parameters:** - `lmp` (query, optional, string) — LMP (or conception/due_date) Example: `2025-01-01` - `as_of` (query, optional, string) — Reference date (default today) Example: `2025-04-02` **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/pregnancy-api/v1/gestational-age?lmp=2025-01-01&as_of=2025-04-02" ``` **Response:** ```json { "data": { "lmp": "2025-01-01", "as_of": "2025-04-02", "basis": "last menstrual period", "overdue": false, "due_date": "2025-10-08", "trimester": "second", "days_remaining": 189, "gestational_age": "13w 0d", "progress_percent": 32.5, "gestational_weeks": 13, "gestational_total_days": 91, "gestational_days_into_week": 0 }, "meta": { "timestamp": "2026-06-03T17:42:10.558Z", "request_id": "b16c4084-e0c0-4d4a-aefa-9c39b6bc28b0" }, "status": "ok", "message": "Gestational age", "success": true } ``` #### `GET /v1/milestones` — Key pregnancy milestones **Parameters:** - `lmp` (query, optional, string) — LMP (or conception/due_date) Example: `2025-01-01` **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/pregnancy-api/v1/milestones?lmp=2025-01-01" ``` **Response:** ```json { "data": { "lmp": "2025-01-01", "basis": "last menstrual period", "due_date": "2025-10-08", "milestones": [ { "date": "2025-04-02", "week": 13, "milestone": "End of first trimester" }, { "date": "2025-07-09", "week": 27, "milestone": "End of second trimester" }, { "date": "2025-06-18", "week": 24, "milestone": "Viability (24 weeks)" }, { "date": "2025-05-07", "week": 18, "milestone": "Anatomy scan window start (18 weeks)" }, { "date": "2025-07-16", "week": 28, "milestone": "Third trimester begins (28 weeks)" }, { "date": "2025-09-17", "week": 37, "milestone": "Preterm threshold (37 weeks / full term)" }, { "date": "2025-09-17", "week": 37, "milestone": "Early term (37–38 weeks)" }, { "date": "2025-10-01", "week": 39, "milestone": "Full term (39–40 weeks)" }, { "date": "2025-10-08", "week": 40, "milestone": "Due …(truncated, see openapi.json for full schema) ``` ### Meta #### `GET /v1/meta` — Spec **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/pregnancy-api/v1/meta" ``` **Response:** ```json { "data": { "name": "Pregnancy Due Date API", "notes": "Naegele's rule: due date = LMP + 280 days; conception assumed at LMP + 14 days. Informational, not medical advice. Nothing is stored.", "version": "v1", "endpoints": [ { "path": "/v1/due-date", "params": { "lmp": "last menstrual period YYYY-MM-DD", "due_date": "or a known due date", "conception": "or conception date" }, "returns": "due date, conception estimate and fertile window" }, { "path": "/v1/gestational-age", "params": { "lmp": "or conception / due_date", "as_of": "reference date (default today)" }, "returns": "gestational age, trimester, days remaining and progress" }, { "path": "/v1/milestones", "params": { "lmp": "or conception / due_date" }, "returns": "the key pregnancy milestone dates" }, { "path": "/v1/meta", "params": [], "returns": "this document" } ], "description": "Pregnancy and due-date maths as an API, using the standard Naegele's rule (40 weeks / 280 days from the last menstrual period). The due-date …(truncated, see openapi.json for full schema) ``` --- Marketplace page: https://www.oanor.com/api/pregnancy-api OpenAPI spec: https://www.oanor.com/api/pregnancy-api/openapi.json