Sprint 7 Health Hub
Period Tracker (Static/Local)
Local-only log saved in your browser.
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How it works
The Period Tracker helps you log menstrual cycle start dates, calculate your average cycle length, predict upcoming period dates, and estimate your fertile window — all stored locally in your browser, never uploaded to any server.
What the tracker records and predicts: - **Cycle start dates**: log each period start date — the tracker builds history over time - **Average cycle length**: calculated from your logged history (more accurate with 3+ cycles) - **Period duration**: average number of days of bleeding (used for end-of-period predictions) - **Next predicted period**: based on your average cycle length from the last logged start date - **Fertile window estimate**: days 10–17 of a 28-day cycle (adjusted proportionally for your actual cycle length). The fertile window is the 6-day window ending on ovulation day — typically cycle length minus 14 days from start. - **Ovulation day estimate**: approximately 14 days before the next expected period
Important limitations: Cycle predictions are averages — individual cycles vary by several days even for people with "regular" cycles. The fertile window calculation is based on the calendar method and is not a reliable contraceptive method. For conception planning or contraception, consult a healthcare provider about more precise methods (basal body temperature tracking, ovulation predictor kits, cervical mucus monitoring).
Privacy is the core feature of this tracker: all data is saved in your browser's localStorage. It is never uploaded, synced, or transmitted anywhere. Clearing your browser data will clear your tracking history — export your log regularly as a backup.
Privacy: all data stored locally in browser localStorage. Zero data transmission.
Frequently Asked Questions
- Prediction accuracy depends entirely on cycle regularity. For people with consistently regular cycles (varying by 1–2 days), predictions within 2–3 days are typical after 3+ logged cycles. For people with irregular cycles (varying by 5+ days), predictions become wide-range estimates rather than specific dates. The tracker uses your average cycle length from all logged cycles — more data always improves accuracy. If your cycles vary significantly month to month, note that no calendar-based method will produce precise predictions.
- No. The calendar-based fertile window estimate is not a reliable contraceptive method. It's based on population averages and assumes consistent ovulation timing, which is affected by stress, illness, travel, hormonal fluctuations, and other factors. The fertility awareness method (FAM) for contraception requires tracking multiple indicators simultaneously (basal body temperature, cervical mucus, and cycle length) and professional instruction — calendar tracking alone has a typical-use failure rate of approximately 24% per year. Consult a healthcare provider for contraceptive guidance.
- Your period tracking data is stored in your browser's localStorage — clearing browser data, cookies, or site data will permanently delete your tracking history. To protect your data: use the Export function periodically to download your log as a CSV file. This file can be re-imported into the tracker or kept as a personal health record. The tracker does not sync to any cloud service, which provides maximum privacy but means data protection is entirely your responsibility.
- Menstrual cycle length varies for many physiological and environmental reasons: stress (increases cortisol, which disrupts the hypothalamic-pituitary-ovarian axis), significant changes in body weight, intense exercise, sleep disruption, illness, travel across time zones, and hormonal fluctuations. Cycles are measured from the first day of one period to the first day of the next — typical healthy variation is 21–35 days, with variation of up to 7–9 days between cycles being common even in otherwise healthy people.