BabyData Pregnancy Calculators

npx add-mcp 'https://babydata.co.uk/mcp'

Data API and MCP server

BabyData exposes its baby-and-pregnancy calculators as a free, read-only JSON API and a Model Context Protocol (MCP) server, so an AI agent gets the same numbers from the same rules as the on-page tools. The endpoints cover due date, ovulation, pregnancy weeks and UK statutory maternity pay. Every response returns the rule it used and a primary UK source. No authentication, no PII, licensed CC BY 4.0. Pregnancy outputs are informational only, not medical advice, and are written using NHS and gov.uk guidance.

Informational only, not medical or financial advice. These tools return estimates, not diagnoses or guarantees. Confirm pregnancy questions with your midwife, GP or NHS 111, and statutory pay on gov.uk.

REST endpoints

All endpoints are GET, return JSON, and accept query parameters. Dates are YYYY-MM-DD.

GET /api/due-date

Estimate a due date and current pregnancy stage (Naegele’s rule).

Parameters: method (lmp, conception, ivf), date (YYYY-MM-DD), embryoAge (IVF), asOf

Example: /api/due-date?method=lmp&date=2026-01-15

GET /api/ovulation

Estimate ovulation day, the fertile window and the next period.

Parameters: lastPeriod (YYYY-MM-DD), cycleLength (20 to 45, default 28)

Example: /api/ovulation?lastPeriod=2026-01-15&cycleLength=28

GET /api/pregnancy-weeks

How many weeks pregnant, with trimester and progress.

Parameters: lmp or dueDate (YYYY-MM-DD), asOf

Example: /api/pregnancy-weeks?lmp=2026-01-15

GET /api/maternity-pay

Estimate UK Statutory Maternity Pay over the 39 weeks (gov.uk rule).

Parameters: weeklyEarnings or annualSalary (GBP)

Example: /api/maternity-pay?weeklyEarnings=600

MCP server

A Model Context Protocol server is available at /mcp (streamable-http, JSON-RPC 2.0, protocol version 2025-06-18). It exposes the same four calculators as MCP tools:

• calculate_due_date
• calculate_ovulation
• pregnancy_weeks
• maternity_pay

The MCP manifest is at /.well-known/mcp.json and the OpenAPI 3.1 description at /openapi.json.

Methods and sources

Each response carries the rule it applied. Due dates use Naegele's rule (LMP plus 280 days, conception plus 266, IVF transfer plus 266 minus embryo age), as the NHS dates pregnancy. Ovulation is cycle length minus 14, with the fertile window the 5 days before ovulation plus ovulation day. Statutory Maternity Pay follows the gov.uk rule: 6 weeks at 90% of average weekly earnings, then 33 weeks at the lower of the flat rate or 90%. The names and births data draws on the ONS Baby names in England and Wales dataset, ONS births, National Records of Scotland and NISRA.

Terms

Read-only, no authentication, no personal data is stored. Licensed under CC BY 4.0: reuse the figures with attribution to BabyData. The maternity pay calculator uses the 2026-27 gov.uk flat rate of £194.32 a week, which changes each April.

OM

Oliver Mackman

Editor, BabyData

Oliver Mackman is the named editor of BabyData and a director of Best Business Loans Ltd (Companies House 16833937), the company that operates the site. He is accountable for its editorial standards, sourcing and corrections, and requires every number to cite the underlying rule and the official UK dataset behind it, with pregnancy tools written using NHS and gov.uk guidance.

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