Period Calculator

A normal menstrual cycle ranges from 21 to 35 days, with an average of 28 days. The period itself typically lasts 3–7 days. Cycle length can vary by a few days from month to month — this is normal. Cycles shorter than 21 days (polymenorrhea) or longer than 35 days (oligomenorrhea) may be worth discussing with a doctor, especially if they're a change from your usual pattern.

Common causes of a late period: (1) Pregnancy — if there's any chance of conception, take a test; (2) Stress — physical or emotional stress can delay ovulation; (3) Weight changes — significant weight loss or gain disrupts hormones; (4) Illness or intense exercise; (5) Thyroid issues; (6) PCOS (polycystic ovary syndrome); (7) Perimenopause (usually 40s–50s). An occasional late period (up to 7 days) is normal. Consistently late or missed periods warrant medical evaluation.

Period calculators are estimates based on average cycle patterns. They work best when your cycles are regular and consistent. Most people with regular cycles will have their period within ±3 days of the predicted date. For irregular cycles, the calculator becomes less accurate. Factors like stress, illness, travel, and hormonal changes can shift your cycle. For medical decisions or fertility planning, track your cycle manually over several months for a more accurate baseline.