Period Tracker & Calculator (Private)

About the Period Tracker & Calculator (Private)

A period tracker that keeps your data on your own device. Log the first and last day of each period, the heaviest flow and any symptoms, and it learns your average cycle to predict your next periods, fertile window and ovulation day on a calendar. It also checks your cycles against the normal limits of FIGO (the International Federation of Gynecology and Obstetrics) — or ACOG’s for teenagers — and says plainly what is worth mentioning to a doctor.

There is no account and no server: the log is stored in this browser’s own database and never uploaded. You can encrypt it with a passphrase, export a backup file, import it on another device, or delete everything with one button. Quick predict gives a forecast from a single date without saving anything. Predictions are estimates and not a method of contraception.

How the predictions work

• Cycle length is counted from the first day of one period to the first day of the next. The tracker averages your last six cycles; until you have logged two periods it assumes 28 days (you can change that).
• Next period = first day of your last period + your average cycle.
• Ovulation is estimated 14 days before the next period (set your own luteal phase if you know it) and the fertile window is the six days ending on that day — the days in which all pregnancies began in a study of 221 women trying to conceive (Wilcox et al.).
• Gaps of more than 90 days between logged periods are left out of the averages, because they usually mean a period was not logged.
• A late period: once the expected day has passed, the tracker says how many days late the period is and stops showing later predictions and a next fertile window — they would assume a period that has not come. Log the period when it starts.

Ovulation can come earlier or later than any average predicts, even in regular cycles, so treat the fertile window as an estimate.

What the cycle check looks for

For adults it uses FIGO’s 2018 definitions of normal menstrual bleeding:

• Frequency: a period every 24–38 days (more often is “frequent”, less often “infrequent”).
• Regularity: the shortest and longest cycles differ by no more than 7–9 days — 9 days at ages 18–25 and 42–45, 7 days at 26–41 (add your age in Settings for the exact limit). The check needs at least three cycles.
• Duration: bleeding for 8 days or less.
• Volume: heavy menstrual bleeding is defined by its effect rather than by an amount — in the words of NICE, excessive menstrual blood loss that interferes with a woman’s physical, social, emotional and/or material quality of life. Bleeding between periods is also listed as abnormal uterine bleeding.

For girls and teenagers (under 18) it uses ACOG’s guidance instead: cycles typically 21–45 days, bleeding for 7 days or less, while periods 90 days apart even once, bleeding for more than 7 days, soaking more than one pad or tampon every 1–2 hours, or heavy periods with a history of excessive bruising or bleeding (or a family history of a bleeding disorder) may need evaluation.

None of these is a diagnosis — they are good reasons to talk to a doctor, and your log (or its CSV) is useful to show them.

Your data and privacy

• The log lives in an IndexedDB database called tv-period-tracker in this browser on this device (it is also listed, and can be deleted, on the cookies and storage page). MySmartCoPilot has no copy and no account system for it; the page works offline once loaded.
• Passphrase protection encrypts the log with AES-256-GCM using a key derived from your passphrase with PBKDF2-SHA-256 and 600,000 iterations (the OWASP recommendation), with a fresh random IV every time it is saved. The passphrase is never stored: if you forget it, the data cannot be recovered.
• Backups are JSON files you download yourself — encrypted when a passphrase is set, readable otherwise. Download CSV gives a readable table for your own records or your doctor. Delete all tracker data removes the database from this browser.
• Nothing is stored until you save your first entry, so Quick predict leaves nothing behind. With the tracker open in two tabs, each picks up changes saved in the other, so an old tab cannot overwrite newer entries.
• Clearing your browser’s site data deletes the log. Safari also deletes a site’s stored data after seven days of Safari use without your interacting with the site (WebKit, 2020); a site added to the Home Screen keeps its own count. Open the tracker regularly or export a backup.

Sources

• Munro MG, Critchley HOD, Fraser IS; FIGO Menstrual Disorders Committee. The two FIGO systems for normal and abnormal uterine bleeding symptoms and classification of causes of abnormal uterine bleeding in the reproductive years: 2018 revisions. Int J Gynaecol Obstet 143(3):393-408 — limits as summarised in, for example, Nat Rev Endocrinol and Medicina
• ACOG. Menstruation in Girls and Adolescents: Using the Menstrual Cycle as a Vital Sign, Committee Opinion 651
• Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. N Engl J Med 333(23):1517-21 · Wilcox AJ, Dunson D, Baird DD. The timing of the “fertile window”. BMJ 321:1259-62
• NICE. Heavy menstrual bleeding: assessment and management, NG88 — Context
• OWASP. Password Storage Cheat Sheet (PBKDF2-HMAC-SHA256: 600,000 iterations) · WebKit. Full Third-Party Cookie Blocking and More (the 7-day cap on script-writable storage)

Limitations

• Predictions are averages: not a method of contraception, and not a way to tell whether you are pregnant.
• It assumes natural cycles. If you use hormonal contraception, are pregnant or breastfeeding, or are near the menopause, its predictions may not apply.
• The log is kept in one browser on one device and does not sync. Export a backup to move it or keep it safe.
• Up to 3,000 entries, dates within the last 10 years, periods of up to 31 days and spotting episodes of up to 14 days.

Privacy

Everything you log stays in this browser’s own storage on this device, optionally encrypted with your passphrase. Nothing is sent to MySmartCoPilot or anyone else; backups are files you download yourself, and “Delete all tracker data” removes the log from this browser.