Period & Ovulation Calculator
How the calculation works
The classic model assumes ovulation occurs 14 days before the next period (luteal phase length). For a 28-day cycle that means day 14; for a 30-day cycle, day 16. The fertile window spans roughly 5 days before ovulation through 1 day after, since sperm can survive up to 5 days in the reproductive tract.
This model is approximate. Real cycles vary by ±2 days even in regular cyclers, and stress, travel, illness, or PCOS can shift ovulation significantly.
Frequently Asked Questions
What is the fertile window?
The 5 days before ovulation plus ovulation day itself. Conception is most likely on the 2 days before and day of ovulation.
Why is my ovulation day not always the same?
Hormone levels fluctuate. Tracking ovulation signs (cervical mucus, basal body temperature, LH urine tests) gives a more accurate picture than calendar math alone.
Can I use this for birth control?
No. Calendar-based methods have failure rates of 12–24% per year. Use proper contraception if pregnancy is not desired.