Period Calculator & Next Period Predictor

Enter the first day of your last period and your average cycle length (28 days is typical, but 21–35 days is also normal). The calculator counts forward to predict your next 6 period start dates, plus the ovulation day and fertile window within each cycle. The prediction assumes a roughly regular cycle.

Any cycle between 21 and 35 days is considered normal. The 28-day cycle is a popular average, not a universal standard. What matters more is consistency — if your cycle length varies by less than 7–9 days month to month, you're considered regular.

It gives a rough estimate, but predictions are less accurate when cycles vary. With PCOS, post-pregnancy, perimenopause, or chronic stress, cycles often shift by 7+ days. For irregular cycles, track 3–6 months of actual dates to find your personal average, and don't rely on calendar predictions for contraception.

No — it's a calendar tool. If you have heavy bleeding, severe pain, missed periods for 3+ months (when not pregnant), bleeding after menopause, or any new symptoms, see a gynaecologist. The calculator helps you track your cycle; it doesn't diagnose conditions.

A period is officially 'late' once you're 5+ days past your expected date. Common reasons include stress, sudden weight change, intense exercise, travel, hormonal changes, thyroid issues, PCOS, perimenopause, and pregnancy. If you're sexually active and your period is late, take a home pregnancy test 1–2 weeks after the missed period for the most accurate result.

Shorter cycles (21–23 days) can occasionally produce two periods within a calendar month — normal if consistent. But unexpected bleeding between periods, very heavy or prolonged bleeding, or bleeding after intercourse can indicate hormonal imbalance, fibroids, polyps, or thyroid issues — book a gynaecologist appointment if it happens more than once.