Menstrual Cycle
Track Menstrual Cycle by entering your cycle dates and temperatures. Get predicted ovulation window, fertile days, and cycle phase breakdown.
Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
Formula
Ovulation = Cycle Length - 14 days
Ovulation typically occurs 14 days before the next period. The fertile window is 5 days before through 1 day after ovulation.
Worked Examples
Example 1: Calculate Next Period
Problem:Last period started Jan 15, cycle length 30 days.
Solution:Last period: January 15 Cycle length: 30 days Next period = Jan 15 + 30 days = February 14 Ovulation day = 30 - 14 = day 16 Ovulation date = Jan 15 + 16 = January 31 Fertile window: January 26 - February 1
Result:Next period: February 14, Ovulation: January 31
Example 2: Determine Fertile Window
Problem:28-day cycle, last period Jan 1.
Solution:Cycle length: 28 days Ovulation day: 28 - 14 = day 14 Ovulation date: January 14 Fertile window: 5 days before: January 9 Ovulation day + 1: January 15 Most fertile: January 12-14 (2 days before through ovulation day)
Result:Fertile window: January 9-15
Example 3: Track Cycle Day
Problem:Last period Feb 1, today is Feb 20, 26-day cycle.
Solution:Last period: February 1 Today: February 20 Days since last period: 19 Cycle day: 19 (if within first cycle) For 26-day cycle: Ovulation around day 12 (26-14) Currently in luteal phase Next period: Feb 1 + 26 = February 27
Result:Day 19 of cycle (luteal phase)
Frequently Asked Questions
How long is a normal menstrual cycle?
Normal cycles range from 21-35 days, with 28 days being average. Cycles are measured from the first day of one period to the first day of the next. Variation of a few days between cycles is normal. Consistently irregular cycles may warrant medical evaluation.
How accurate are period calculators?
Calculators provide estimates based on average cycle patterns. They're most accurate for regular cycles. Actual ovulation can vary by several days. For pregnancy planning or avoidance, combine with other fertility awareness methods (temperature, cervical mucus) or use contraception.
What causes irregular cycles?
Common causes: stress, weight changes, excessive exercise, PCOS, thyroid disorders, perimenopause, breastfeeding, starting/stopping birth control. Occasional irregularity is normal. Consistently irregular cycles (varying by more than 7-9 days) should be evaluated by a healthcare provider.
What are the phases of the menstrual cycle?
1) Menstrual (days 1-5): Uterine lining sheds. 2) Follicular (days 1-13): Egg develops in ovary, estrogen rises. 3) Ovulation (day 14): Egg released. 4) Luteal (days 15-28): Progesterone rises, uterus prepares for potential pregnancy.
How do birth control pills affect cycles?
Hormonal birth control regulates or suppresses the natural cycle. Combined pills prevent ovulation and create predictable withdrawal bleeding. Some pills eliminate periods entirely. After stopping, it may take 1-3 months for natural cycles to resume.
When should I see a doctor about my cycle?
Consult a doctor if: periods stop for 3+ months (not pregnant), cycles shorter than 21 or longer than 35 days consistently, extremely heavy bleeding, severe pain interfering with daily life, bleeding between periods, or sudden changes in cycle pattern.