Period Calculator
Predict your next period, track your menstrual cycle, find your fertile window, and plan ahead with accurate predictions based on your cycle history. Calculate ovulation dates and understand your cycle phases.
Select the first day your last period started
Average days from first day of one period to first day of next
How many days your period typically lasts
What is a normal menstrual cycle length?
Normal cycle: 21-35 days (average 28 days), measured from first day of period to day before next period starts. Period duration: 2-7 days (average 3-5 days). Variations are normal: Cycles can vary by 2-3 days month to month, stress/travel/illness can affect timing, first few years after menarche often irregular, approaching menopause cycles become irregular. Concerning signs: Cycles <21 or >35 days consistently, bleeding >7 days, very heavy flow (changing pad/tampon every 1-2 hours), severe pain interfering with daily life. Track for 3+ months to identify patterns. Consult doctor if consistently irregular.
When am I most fertile during my cycle?
Fertile window: 5-6 days (5 days before ovulation + day of ovulation). Ovulation typically occurs: Day 14 of 28-day cycle, or ~14 days before next period (regardless of cycle length). Most fertile days: 2-3 days before ovulation (sperm survives up to 5 days, egg survives 12-24 hours). Signs of ovulation: Increased cervical mucus (clear, stretchy, egg-white consistency), slight temperature rise (0.5-1°F), mild cramping on one side, increased libido. Not reliable for birth control: Ovulation timing can vary. For pregnancy: Have intercourse every 2-3 days during fertile window. Use ovulation tests or basal body temperature tracking for better accuracy.
Why is my period late or irregular?
Common causes of late/irregular periods: Stress (physical or emotional) - disrupts hormone balance, Weight changes (loss or gain >10 lbs) - affects estrogen production, Excessive exercise (athletes, intense training) - reduces body fat below threshold, PCOS (Polycystic Ovary Syndrome) - hormonal imbalance, very common, Thyroid disorders (hypo/hyperthyroidism), Medications (antidepressants, blood thinners, steroids), Pregnancy or breastfeeding, Approaching menopause (perimenopause). When to see doctor: Missed 3+ periods, suddenly irregular after being regular, severe pain, very heavy bleeding, age >15 without period starting. Track cycles for 3 months before appointment.
How can I predict my next period accurately?
Prediction methods: Track at least 3 cycles to find YOUR average (may not be 28 days), Use period tracking app (Flo, Clue, Period Tracker), Calculate average cycle length (add all cycles ÷ number of cycles), Note patterns (stress weeks, certain times of month). Improve accuracy: Track symptoms (mood, cramps, bloating, discharge), Note first day of each period, Measure cycle length (first day to day before next period), Consider life factors (travel, stress, diet changes). Reality: 20-30% variation is normal even with regular cycles. Apps predict based on YOUR data, not generic 28-day cycle. Predictions become more accurate after tracking 6+ months.
What are PMS symptoms and when do they occur?
PMS (Premenstrual Syndrome) occurs 1-2 weeks before period (luteal phase). Physical symptoms: Bloating, breast tenderness, headaches, fatigue, acne breakouts, food cravings (especially sweets/salt), cramping (before period starts). Emotional symptoms: Mood swings, irritability, anxiety, depression, difficulty concentrating, crying easily, social withdrawal. PMDD (severe PMS): Debilitating symptoms interfering with life - see doctor. Managing PMS: Regular exercise (reduces symptoms 50%+), reduce caffeine/alcohol/salt, eat small frequent meals, adequate sleep, stress management, calcium/magnesium supplements, track symptoms to predict/prepare. Treatment: Birth control pills, pain relievers, antidepressants (for PMDD).