An animated, single-page walkthrough of weekwise: how one date — the first day of your last period, or a due date from a scan — becomes your gestational age today and a dated, tickable, cited week-by-week schedule of scan windows, ANC visits and Td doses, entirely in your own browser.
- This explainer: https://sreenivas-sadhu-prabhakara.github.io/weekwise-explained/
- The live app it explains: https://sreenivas-sadhu-prabhakara.github.io/weekwise/ (app source)
Informational only — not medical advice. Your obstetrician or midwife overrides this chart. An EDD is an estimate (only about 1 in 20 births land on it). weekwise, and this explainer, never predict labour or replace clinical care. See the full Disclaimer below.
- The due date —
EDD = LMP + 280 days(the 280-day form of Naegele's rule), animated, and how a dating-scan EDD overrides LMP dating. - Age today — gestational age as weeks + days, shown as the single lit bead on the 40-bead week strand, plus trimester and days to the EDD.
- Dated, cited windows — how a published window (e.g. the NHS anomaly scan at 18+0–20+6 weeks = days 126–146 from LMP) becomes your calendar dates, tagged upcoming / open / passed / done, each row cited to MoHFW India or NHS England.
- Tick & hand off — ticking fills the bead solid blush; one page prints as a clean A4 clinic sheet (your browser's print-to-PDF, no library, no upload).
- Private by construction — an animated diagram of a request bouncing off
connect-src 'none': the browser itself blocks any send. It is policy, not promise.
Plus honest limits and an FAQ. Animation is pure CSS + inline SVG (no libraries — the CSP
forbids external and inline scripts beyond app.js). prefers-reduced-motion collapses every
animation to its final, fully legible state. Light and dark themes are both WCAG-AA; everything
is keyboard-operable with a skip link and visible focus rings.
Every date the page shows is derived at load time by the same 280-day / day-offset
arithmetic the weekwise app uses — never hand-typed. The worked example (LMP 2026-01-05,
EDD 2026-10-12, "today" pinned to 20+0 weeks = 2026-05-25) and each milestone window are
re-derived in data/facts.js and asserted in test/facts.test.js, which also
cross-checks against the real weekwise engine when the app repo sits beside this one.
No build step, no dependencies.
git clone https://github.com/Sreenivas-Sadhu-Prabhakara/weekwise-explained.git
cd weekwise-explained
open index.html # or serve statically: python3 -m http.server 8000Run the self-tests (Node 20+):
node --testThe tests re-derive the due-date and gestational-age arithmetic, check leap-day handling,
re-date every example milestone window and its status, and (if ../weekwise is present)
confirm the explainer's numbers match the app's engine exactly.
Same guarantee as the app it explains: this page ships a strict Content-Security-Policy with
connect-src 'none', so the browser itself blocks every network request. No server, no
account, no analytics, no external fonts or scripts. The only thing stored is your theme
choice, in this browser's localStorage.
This explainer and the weekwise app are informational tools provided "as is," without warranty of any kind, and are not medical advice. Your obstetrician, midwife or paediatrician overrides the chart. An estimated due date (EDD) is an estimate, not a prediction — only about 4.4% of babies arrive on it (Royal Berkshire NHS Foundation Trust, May 2026) — and these tools never predict labour or replace clinical care. They show a dated snapshot of published MoHFW India and NHS England schedule windows; guidelines change, so confirm current advice at your clinic, and no interpretation is given beyond the cited windows. Routine singleton pregnancies only; multiple, IVF and high-risk pregnancies follow different plans not modelled here. The hospital record / MCP card remains the record of truth. The author accepts no liability for decisions made using these tools.
MIT © 2026 Sreenivas Sadhu Prabhakara