Tracking your period takes exactly one habit: log the first day of full flow each time it starts. This page turns that log into your average cycle, regularity check, and next-period prediction — stored only in this browser, on this device.
Because your cycle is a health signal, not just a schedule: clinicians treat the menstrual cycle as a vital sign (ACOG Committee Opinion 651). A dated log turns “my periods feel off” into evidence a doctor can act on — and it catches changes early, when they are easiest to explain.
It is also plainly practical: knowing your window lets you plan travel, supplies and downtime around up to 8 days of flow (FIGO normal range). And since an estimated 14–25% of women have irregular cycles (NICHD), many people are guessing without a log — the record is what replaces guessing.
The entire method is one line: write down day 1, every time. Day 1 is the first day of full flow, not spotting. Everything else — cycle length, average, regularity, next-period prediction — is arithmetic on those dates, and the tracker above does it for you after each log:
From the stats card you can hand your numbers straight to the late period calculator or cycle length calculator without retyping.
Your log is stored in this browser's local storage — on this device, full stop. There is no account, no server-side database, and nothing to sync, leak, or subpoena. Deleting an entry here deletes it everywhere, because "everywhere" is one place. The trade-off: no cross-device sync. If you switch devices, use Export CSV and re-enter your dates there. Details in the privacy policy. This on-device model is the one privacy-conscious users moved to after 2022 — the same trade-off, without the app.
Log the first day of full flow each time. Cycle lengths are the gaps between those dates; the average is their mean. This page automates the arithmetic and keeps the log on your device.
Only in your browser's local storage, on your own device. The site never receives your dates; clearing site data deletes the log permanently.
A practical rule: 3 logged periods for a rough average, 6+ for a reliable one — a rule of thumb for the arithmetic, not a medical threshold. Don’t reset your picture over a single unusual cycle.
Yes — Export CSV downloads your dates as a plain file for any spreadsheet.
Per-entry delete buttons, or Clear all. Data lives only in your browser, so deleting it here deletes it everywhere.
No — sync needs an account and a server, exactly what this tracker avoids. Use CSV export to move your log manually.
Yes — irregular cycles benefit most from tracking. Watch the shortest/longest spread; beyond about 7–9 days, the irregular period calculator fits you better than a single average.
Marking period start dates on a calendar and counting the gaps — the oldest method there is. This tracker is that method with the arithmetic automated.
Your cycle is a health signal clinicians treat as a vital sign (ACOG Committee Opinion 651) — a log turns “my periods feel off” into dates a doctor can act on. It’s also practical: knowing your window lets you plan travel, supplies and downtime around up to 8 days of flow (FIGO). And irregular cycles are common — 14–25% of women have them (NICHD) — so many people are guessing without a log.
Book a visit if your log shows: cycles consistently shorter than 24 or longer than 38 days (FIGO adult range); bleeding lasting more than 8 days; 90 days with no period (secondary amenorrhea); or a year-over-year spread beyond 7–9 days. For teens: cycles of 21–45 days are normal in the first years, but no first period by age 15 warrants evaluation (ACOG 651).
Because ovulation shifts, and the prediction is only as stable as your ovulation day. In 600,000+ real cycles the luteal phase held at 10–15 days while most variation came from the follicular phase (npj Digital Medicine, 2019). A prediction assumes this cycle matches your average; when ovulation runs early or late, the period follows. The log’s value is the history, not any single predicted date.
Three things clinicians ask about that dates alone don’t capture: flow (light/normal/heavy and how many days — ≤8 days is the FIGO normal limit), cramps or pain that disrupts your day, and mood changes that repeat in the same cycle phase. This tracker stores dates; jot the rest in the same place each cycle — a note on your phone works. Patterns across 3+ cycles are what turn symptoms into useful information.
Yes — no account and on-device storage suit a first tracker, and early cycles need patience rather than prediction: teen cycles of 21–45 days are normal while the cycle matures (ACOG Committee Opinion 651), so expect wide swings in the first years. One flag: no first period by age 15 is the standard point for medical evaluation.