Are my health numbers uploaded to a server?

No. HealthTools is 100% client-side. Every calculation — BMI, BMR, body fat, ovulation — runs in your browser as plain JavaScript. There is no backend and no /api route. The Content-Security-Policy (connect-src 'self') even restricts which hosts the page may contact, so the privacy guarantee is enforced by the browser itself.

Are these calculations accurate?

Each calculator uses a standard, published method for its problem — the WHO BMI bands, the Mifflin-St Jeor equation, the US Navy body-fat method, Naegele's rule for the due date, and so on. A verify suite hand-checks reference values against the implemented math before every build. Still, these are educational estimates, not medical advice; consult a qualified professional for any health decision.

Why does the BMI calculator show two classifications?

People of Asian descent face metabolic risk at a lower BMI, so the WHO recommends Asian-Pacific cutoffs (≥23 overweight, ≥25 obese) alongside the standard Western bands (≥25 overweight, ≥30 obese). We show both so you can compare, which is especially relevant for a Hong Kong audience.

Where do the Cantonese food calories come from?

The food calorie database is a curated, build-time static snapshot bundled same-origin in the repo — it never makes a runtime request to any server. Values are approximate, drawn from public nutrition references, and you can refine them over time. Use them as a guide to portion sizes, not an exact count.

Does it work offline?

Yes. After the first load the app shell is cached, so every calculator works with no internet connection. Install HealthTools as a PWA and it opens and runs offline.

Fertility

Ovulation & Due Date Calculator

Fertile window, next ovulation date, and an estimated due date from your last period and cycle length.

Ovulation & Due Date Calculator

Fertile window, ovulation day, next period, and estimated due date.

Last period start

Cycle length

days

Luteal phase

days

Your health numbers never leave your device — all math runs in your browser.

Result

Estimated ovulation

15 Jan 2026

most fertile day

Fertile window10 Jan 2026 – 16 Jan 2026

Next period (est.)29 Jan 2026

Estimated due date8 Oct 2026

Ovulation falls a fixed luteal-phase length before the next period. The fertile window opens ~5 days before (sperm viability) and closes ~1 day after (egg viability).

Ovulation = LMP + (cycle − luteal phase); due date = LMP + 280 days (Naegele). Cycles vary month to month; these are estimates. Educational estimate only — not medical advice. See a qualified professional for decisions about your health.

Printable PDF report, saved profiles & meal-plan compare are Pro features.

One-time unlock, no subscription. Unlock HealthTools Pro →

How to use this calculator

Enter the first day of your last period.
Enter your average cycle length (typically 21–35 days).
Optionally adjust the luteal phase (typically ~14 days).
Read your fertile window, ovulation day, next period, and estimated due date.

Bookmark Ovulation & Due Date Calculator — it works offline once loaded. Educational estimate only — not medical advice. See a qualified professional for decisions about your health.