Predict your next period, fertile window, and ovulation day. All data stays on your device — nothing is uploaded or shared.
🔒 Your data is saved only in your browser (localStorage). Nothing leaves your device.
Know when to expect your period up to 6 months in advance — pack accordingly, schedule events, and never be caught off guard.
Whether you're trying to conceive or just want to understand your body, your fertile window is marked clearly on the calendar.
No app to install, no account to create, no health data sent to any server. Everything stays in your browser — period.
A typical menstrual cycle runs 21 to 35 days in adults, and the average is closer to 29 days than to the 28 commonly quoted. Considerable variation is normal: large studies using tracking data find that most people experience cycle-length differences of several days between consecutive cycles, and perfectly regular cycles are the exception rather than the rule.
The luteal phase, from ovulation to the next period, is the more consistent part at roughly 12 to 14 days. Most variation comes from the follicular phase before ovulation, which is why cycles lengthen or shorten mainly through a delayed or early ovulation rather than a changed second half.
Cycles are also affected by illness, travel, sleep disruption, significant stress, weight change and intensive exercise. An occasional unusual cycle is common and not in itself a cause for concern; a persistent change in a previously stable pattern is worth raising with a clinician.
Calendar-based prediction extrapolates from your recorded history, so it is only as good as the regularity of that history and the number of cycles recorded. For someone with variable cycles the prediction window is genuinely wide, and any app presenting a single confident date is overstating what the data supports.
This matters most for the fertile window, which is frequently misunderstood. Sperm can survive up to about five days, and the egg is viable for roughly 24 hours, so the fertile window is around six days ending on the day of ovulation. But ovulation day varies, and research tracking it directly has found that only a minority of cycles ovulate on the day a calendar method predicts.
A tracker is therefore not a contraceptive. Fertility awareness methods that are genuinely effective require daily basal body temperature, cervical mucus observation or hormone testing, formal training, and strict rule-following — and even then have meaningfully higher typical-use failure rates than long-acting methods. Using calendar predictions alone to avoid pregnancy is unreliable. Equally, a prediction that a day is "safe" should not be relied on.
Menstrual and reproductive data is among the most sensitive category of personal information, and it has been the subject of enforcement action — regulators in several jurisdictions have penalised period-tracking apps for sharing data with advertisers and analytics providers. In some legal environments, reproductive health records carry additional risk.
This tracker keeps its data in your browser's local storage on your own device. There is no account, no server copy, and nothing transmitted — which also means it does not sync across devices, and clearing your browser data removes it. That trade favours privacy over convenience deliberately.
Some patterns warrant clinical attention rather than tracking: cycles consistently shorter than 21 days or longer than 35, bleeding lasting more than seven days, bleeding heavy enough to soak through protection hourly, bleeding between periods or after sex, periods stopping for three months or more without pregnancy, or pain that disrupts daily activity. Severe period pain is not something to endure — endometriosis takes years to diagnose on average, partly because pain is normalised. This tool records and projects dates and is not medical advice or a diagnostic instrument.
The fertile window is the days you can get pregnant in a given cycle. Sperm can live up to 5 days in the reproductive tract, and the egg survives ~24 hours after ovulation. So the fertile window is roughly 5 days before ovulation through 1 day after — typically days 10–15 of a 28-day cycle.
If your cycle varies by more than 5–7 days each month, predictions will be less accurate. Log several periods over time so the tracker can use your actual average. For very irregular cycles, consult a healthcare provider.
No. This tracker is for informational purposes only. The fertility awareness method (FAM) as contraception requires specific training and is most effective when combined with other monitoring. Always use proven contraceptive methods if you wish to avoid pregnancy.
Your logged period history is stored in localStorage. Clearing browser data, using private/incognito mode, or switching devices will erase your history. Consider noting your dates elsewhere for backup.
No. Calendar prediction cannot reliably identify the fertile window, since ovulation timing varies substantially between cycles. Effective fertility awareness requires temperature, mucus or hormone tracking with formal training, and even then is less reliable than long-acting methods.
In your browser's local storage on this device only — no account, no server copy, nothing transmitted. It therefore does not sync between devices, and clearing browser data deletes it.