Track your menstrual cycle, predict ovulation, and identify your fertile window with our accurate period calculator.
The menstrual cycle is controlled by hormones and typically lasts between 21-35 days. It consists of four main phases:
The shedding of the uterine lining. Period typically lasts 3-7 days. Estrogen and progesterone are at their lowest levels.
The pituitary gland releases FSH, stimulating follicle growth. Estrogen rises, thickening the uterine lining. Ends with ovulation.
LH surge triggers release of an egg from the ovary. Most fertile period is the 3 days before and including ovulation day.
The corpus luteum secretes progesterone to maintain uterine lining. If no pregnancy occurs, hormone levels drop, leading to menstruation.
| Cycle Length | Percentage of Women | Ovulation Day |
|---|---|---|
| 21 days | 5% | Day 7 |
| 28 days | 30% | Day 14 |
| 30 days | 20% | Day 16 |
| 35 days | 10% | Day 21 |
| Irregular | 35% | Varies |
Note: Only about 30% of women have cycles that consistently fall within the "average" 28-day range. Variations of ±7 days are completely normal.
The fertile window includes the 5 days before ovulation and the ovulation day itself. Here's why:
Consult a healthcare provider if you experience:
A: While unlikely, it's possible if you have short cycles (21-23 days) since sperm can survive up to 5 days and ovulation may occur soon after your period ends.
A> Common causes include stress, weight changes, PCOS, thyroid disorders, perimenopause, breastfeeding, and certain medications. Occasional variations are normal.
A: They're reasonably accurate for women with regular cycles. For irregular cycles, tracking additional signs (BBT, cervical mucus) improves accuracy.
A: Yes, hormonal contraceptives regulate or eliminate natural cycles. These calculations apply to natural menstrual cycles without hormonal contraception.
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