Track your menstrual cycle, predict your next period, and identify your fertile window and ovulation day.
The uterine lining sheds. This is when bleeding occurs, typically lasting 3–7 days.
Hormones stimulate egg development in the ovaries. Estrogen rises, thickening the uterine lining.
A mature egg is released. This is the most fertile time — the egg survives ~24 hours.
Progesterone rises to support potential pregnancy. If no implantation occurs, hormone levels drop and the cycle restarts.
⚕️ Disclaimer: This calculator provides estimates based on average cycle data. It is not a substitute for medical advice and should not be used as a contraceptive method. Consult your healthcare provider for personalized guidance.
The Period Calculator tracks your menstrual cycle, predicts your next period, and estimates your fertile window and ovulation day using your cycle length and last period date, shown on a clear visual calendar.
You enter the date your last period started and your average cycle length. The tool adds your cycle length to that date to estimate upcoming periods, and marks the likely fertile window and ovulation day.
Predictions are estimates based on average cycle length and are most accurate for regular cycles. Cycles naturally vary, so use the results as a guide, not a guarantee.
The fertile window is roughly the five days before ovulation plus ovulation day. For a typical 28-day cycle, ovulation is around day 14; the calculator adjusts this to your cycle length.
Yes. Everything is calculated in your browser — no cycle information is uploaded or stored on a server.