Predict your next period, fertile window, and ovulation day based on your cycle length. 100% private — all calculations happen on your device.
| Phase | Days | What Happens |
|---|---|---|
| Menstrual | Day 1-5 | Uterine lining sheds (period bleeding) |
| Follicular | Day 1-13 | Follicle develops in ovary, estrogen rises |
| Ovulation | Day ~14 | Egg released, most fertile 24 hours |
| Luteal | Day 15-28 | Progesterone rises, uterine lining thickens |
| Cause | Effect on Cycle | Action |
|---|---|---|
| Stress | Delayed or missed periods | Relaxation techniques, lifestyle changes |
| PCOS | Infrequent or prolonged periods | Consult doctor |
| Thyroid Disorders | Heavy, light, or irregular periods | Consult doctor |
| Weight Changes | Delayed ovulation, missed periods | Maintain healthy BMI |
| Excessive Exercise | Skipped periods (amenorrhea) | Reduce intensity, increase calories |
| Birth Control Changes | Irregular for 1–3 months | Normal adjustment, monitor |
| Timing | Physical Symptoms | Emotional Symptoms |
|---|---|---|
| 1–2 weeks before | Bloating, breast tenderness, headaches | Mood swings, anxiety, irritability |
| Days 1–2 of period | Cramps, lower back pain, fatigue | Sadness, food cravings |
| Days 3–5 of period | Symptoms gradually ease | Mood stabilizes |
| After period | Energy returns, skin clears | Positive mood, high energy |
This calculator provides estimates based on average cycle length. Actual cycles can vary due to stress, travel, diet, and hormonal changes. It's most accurate for women with regular cycles (variation ±2 days). For medical decisions, always consult your doctor.
Normal cycles range from 21–35 days. The average is 28 days, but only 10–15% of women have exactly 28-day cycles. What matters most is consistency — a regular 32-day cycle is perfectly normal.
The fertile window is approximately 5 days before ovulation and 1 day after. Sperm can survive up to 5 days in the body, while the egg is viable for only 12–24 hours after ovulation. Peak fertility is 1–2 days before ovulation.
Common causes include stress, significant weight change, PCOS, thyroid disorders, excessive exercise, and starting/stopping hormonal birth control. See a doctor if cycles are consistently outside 21–35 days or if you miss 3+ periods.
Yes, 100%. All calculations happen locally in your browser using JavaScript. Absolutely no health data is sent to any server. Your cycle information stays completely private on your device — we never store or transmit it.
This calculator should NOT be used as a primary method of birth control. The fertile window prediction is an estimate based on averages. Ovulation timing can shift unexpectedly. Consult a healthcare provider for reliable contraception options.
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