Menstrual Cycle Calculator

Your current cycle day equals the number of days since your last period started, plus one. If your period began 7 days ago, you are on cycle day 8.

In a 28-day cycle, ovulation usually occurs around day 14 — approximately 14 days before the next period. For other cycle lengths, subtract 14 from your total cycle length to estimate ovulation day.

The fertile window typically spans 5–6 days: the 5 days before ovulation and ovulation day itself. An egg survives 12–24 hours, but sperm can survive in the reproductive tract for up to 5 days.

The follicular phase is the period from the end of menstruation to ovulation. The pituitary gland releases FSH, stimulating follicle growth in the ovaries. This phase typically lasts 10–16 days.

The luteal phase follows ovulation. The corpus luteum produces progesterone to prepare the uterus for potential implantation. It consistently lasts about 14 days, regardless of overall cycle length.

Irregular cycles can result from stress, weight changes, thyroid disorders, PCOS, intense exercise, or certain medications. If your cycles are consistently irregular, consult a gynecologist.

No. This calculator is an informational tool and should not be used as a method of contraception. Ovulation timing can vary unpredictably. Consult a healthcare provider for contraceptive advice.

A normal cycle lasts 21–35 days. The most common length is 28 days, but any length within this range is considered medically normal.

Normal menstrual bleeding lasts 2–7 days. A period shorter than 2 days or longer than 7 days should be discussed with a gynecologist.

Keep a cycle diary for several months, noting the start date of each period and its duration. This allows you to calculate your average cycle length and more accurately predict future periods and fertile days.