Ovulation and Fertility Window Calculator
Calculate your ovulation day and fertile window based on your last period and cycle length.
Plan for conception or track your cycle.
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Fertility Estimate
Ovulation typically occurs about 14 days before your next period. This is based on the luteal phase, which is relatively consistent at ~14 days for most women.
Key formulas:
Ovulation Day = Last Period Start + (Cycle Length - 14)
Fertile Window = Ovulation Day - 5 to Ovulation Day + 1
Next Period = Last Period Start + Cycle Length
Important notes:
- The fertile window spans about 6 days: the 5 days before ovulation and the day of ovulation itself
- Sperm can survive up to 5 days in the reproductive tract
- The egg is viable for about 12–24 hours after ovulation
- Average cycle length is 28 days, but 21–35 days is considered normal
- This calculator provides estimates only — actual ovulation can vary cycle to cycle
Signs of ovulation:
- Rise in basal body temperature
- Changes in cervical mucus
- Mild pelvic pain (mittelschmerz)
- Positive ovulation predictor kit (OPK)