Informational only — your obstetrician or midwife overrides this chart. An EDD is an estimate (only about 1 in 20 births land on it). weekwise dates the published MoHFW and NHS schedule windows and never predicts labour or replaces clinical care.

weekwise explained

LMP or EDD in · a dated, cited schedule out · offline by construction

Pregnancy due dates, explained — from LMP and 280 days to a dated scan & ANC schedule

weekwise takes one date — the first day of your last period, or a due date from a scan — and turns it into your gestational age today plus a dated, tickable, cited week-by-week schedule of scan windows, ANC visits and Td doses. This page walks through exactly how, with the same arithmetic the app runs and its self-tests prove.

Open weekwise — it's free See how it works ↓
The 40-bead week strand — one bead per week. In the worked example on this page the current week (20+0) is the single filled blush bead; milestone weeks hang small tags.

One date in. A whole dated schedule out.

Pregnancy care runs on a calendar you don't set: a dating scan in a particular fortnight, an anomaly scan in another, antenatal visits and vaccine doses each with their own window. The guidance is public — MoHFW in India, the NHS in England — but it's written in weeks of pregnancy, not in your dates.

weekwise does the one translation that turns weeks into dates: it anchors everything to a single day-zero, then adds. This page follows that translation through five short scenes — due date, age today, dated windows, the clinic handoff, and privacy — using one fixed example so the numbers stay put while you read.

1 The due date

LMP + 280 days = EDD — and a scan can overrule it

Naegele's rule, the 280-day form: forty weeks counted from the first day of your last period. Every date on this page is derived by the same engine the app uses.

Count forward forty weeks

The app assumes a regular 28-day cycle and accurate recall of the last period. It computes in whole days on the calendar — leap years and month-ends included — so there's no drift.

A dating scan measures the pregnancy directly and is more accurate than counting from a period. If you have a scan due date, you enter that as the EDD and the whole timeline recomputes from it — scan dating overrides LMP dating.

Worked from the fixed example LMP 2026-01-05. test/facts.test.js re-derives 2026-10-12 and asserts it.

2 Age today

Gestational age is just today minus day-zero

Weeks and days since the LMP — shown as one lit bead on the 40-bead strand, plus the trimester and the days left to the EDD.

Weeks + days, not a fuzzy month

Days since day-zero, divided by seven: the whole part is the week, the remainder is the day. In the example, 140 days is exactly 20 weeks + 0 days — the single blush-filled bead. Beads before it are threaded solid; beads after it wait, hollow.

weekwise never shows a negative age and never invents a milestone before day-zero. Past 42+0 weeks it stops computing and says so — it does not predict labour.

Example today 2026-05-25 = LMP + 140 days. The engine, not this page, produces “20+0”.

3 Dated, cited windows

Each published milestone becomes your own calendar window

A guideline says “18+0 to 20+6 weeks.” weekwise stores that as days from LMP, adds them to your day-zero, and cites the source. Two tracks — MoHFW India and NHS England — kept separate, never blended.

Offset in, calendar window out

“18+0 to 20+6 weeks” is days 126 to 146 from LMP. Add them to 2026-01-05 and the anomaly-scan window is 2026-05-11 → 2026-05-31.

Each row is tagged against today: upcoming, open now, passed, or done once you tick it. Status is never colour alone — it always carries a word and a shape.

The example timeline, dated from 2026-01-05

    Every date and status here is produced by the engine and asserted in test/facts.test.js — including that the anomaly window is genuinely open on the example day.

    Every row is cited. weekwise transcribes each window verbatim from a staged source and stamps a verified-on date. Examples on the live app:

    • NHS FASP handbook — anomaly scan “18+0 to 20+6 weeks of pregnancy.”
    • MoHFW ANC/SBA Guidelines (2010) — the four-visit ANC schedule.
    • National Immunization Schedule — Td-1 “early in pregnancy,” Td-2 four weeks later.

    Guidelines get revised. weekwise shows a dated snapshot and tells you to confirm current advice at your clinic — it gives no interpretation beyond the cited window.

    4 Tick & hand off

    Tick what's done — then print one A4 sheet for the clinic

    A tick fills the bead solid blush and can carry a done-on date. When you're ready, one page prints — the schedule you actually carry in.

    From a live chart to a paper handoff

    Ticking a row marks it done regardless of its dates — your record of what actually happened wins over the window. Untouched windows that fall behind today show as passed, flagged for you to raise with your provider; the app never reschedules anything and sends no reminders.

    The print view drops the controls and lays out a clean one-page A4 sheet — the printable, carry-to-clinic version of the same dated schedule. No PDF library, no upload: your browser's own print-to-PDF.

    Tick to done
    Prints as a one-page A4 clinic sheet

    5 Private by construction

    “It never leaves your browser” is enforced, not promised

    A pregnancy record is nobody's business but yours. weekwise doesn't just say it won't send your data — it ships a policy that makes the browser itself refuse to.

    your browser localStorage weekwise ✓ connect-src 'none' internet
    Every request the page could make — blocked before it leaves.

    Both the app and this explainer send the browser this policy:

    default-src 'self'; connect-src 'none'
    • No network calls possible — fetch, XHR and WebSockets are refused by the browser, by policy.
    • No server, no account, no analytics — nothing to log in to, nothing watching.
    • localStorage only — your dates, ticks and the name on the sheet live in this browser alone.
    • A JSON backup is the only exit — a file you download on purpose; it's also your only copy across devices.

    The honest flip side: clearing site data or switching devices loses the record. There's no cloud copy — by design. The hospital record or MCP card stays the record of truth.

    What weekwise honestly will not do

    • No clinical advice. Your obstetrician or midwife overrides the chart — it only dates the cited published windows and interprets nothing further.
    • No labour prediction. An EDD is an estimate; only about 4.4% of babies come on it (Royal Berkshire NHS FT, May 2026). The app never guesses your delivery day.
    • No replanning, no reminders. Missed windows show as “passed” for you to raise with your provider; the chart only updates when you open it.
    • Routine singleton pregnancies only. Multiple, IVF and high-risk pregnancies follow different plans the app does not model — the honest override is entering your scan EDD.
    • No fetal-development editorial (“the size of a mango”) — it isn't citable to a guideline window, so it isn't there.

    Questions people ask

    How is the due date calculated from the last period?

    EDD = LMP + 280 days (40 weeks) — the 280-day form of Naegele's rule. It assumes a regular 28-day cycle and accurate LMP recall. A dating-scan EDD is more accurate: enter it directly and the whole timeline recomputes from it.

    How accurate is an estimated due date?

    It's an estimate, not a prediction. Only about 4.4% of babies arrive on their due date (Royal Berkshire NHS FT, May 2026) — fewer than 1 in 20. Pregnancy normally lasts 37 to 42 weeks from the first day of the last period. weekwise never predicts labour.

    How does a “week” window become real dates?

    Each milestone is stored as days from LMP day-zero (e.g. the anomaly scan is days 126–146 for 18+0–20+6 weeks). weekwise adds those offsets to your LMP and marks the window upcoming, open, passed or done against today. Every row is cited to MoHFW or NHS with a verified-on date.

    Does weekwise send my record anywhere?

    No — and it can't. Both the app and this page set connect-src 'none', so the browser itself blocks every network request. No server, no account, no analytics; localStorage only, with a JSON backup as the single, deliberate exit.

    One date in. A dated, cited schedule out.

    Free, offline, MIT-licensed. It runs on the phone already in your pocket — and the record never leaves it. Informational only; your obstetrician or midwife overrides the chart.

    Open weekwise →

    Source code on GitHub