Ovulation Calculator
Estimate your fertile window, ovulation day, and next period based on your last period date and cycle length.
Your data stays in your browser. We do not store, collect, or transmit any information you enter.
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)