Ovulation Calculator
Predict your ovulation date based on cycle length and last period date to identify your most fertile days.
Results
Visualization
How It Works
Ovulation typically occurs 12-14 days before your next period (the luteal phase is fairly constant). The fertile window spans ~6 days around ovulation.
The Formula
Ovulation Day = Cycle Length - Luteal Phase Length
Fertile Window = Ovulation Day - 5 to Ovulation Day + 1
Variables
- Luteal Phase — The phase from ovulation to menstruation — usually 12-14 days
- OPK — Ovulation Predictor Kit — detects LH surge 24-36 hours before ovulation
Worked Example
With a 28-day cycle and 14-day luteal phase: ovulation on Day 14. Fertile window: Day 9-15. Peak: Day 12-14.
Practical Tips
- Sperm can survive up to 5 days in the reproductive tract, but the egg lives only 12-24 hours.
- The most fertile days are the 2-3 days BEFORE ovulation, not the day of.
- Use OPKs (ovulation predictor kits) starting 3 days before expected ovulation.
- Cervical mucus that looks like raw egg whites indicates peak fertility.
- Stress, illness, and travel can shift ovulation even in regular cycles.