Ovulation occurs approximately 14 days before your next period — not 14 days after your last one. This distinction is crucial for accurate ovulation prediction.
The Ovulation Formula
Estimated ovulation day = cycle length − 14. Count from the first day of your last period.
- 24-day cycle: ovulation day 10
- 28-day cycle: ovulation day 14
- 32-day cycle: ovulation day 18
- 35-day cycle: ovulation day 21
Why 14? The luteal phase (ovulation to next period) is remarkably consistent at 12–16 days for most women. The follicular phase (period to ovulation) varies with cycle length. So working backwards 14 days from your expected next period gives a reliable ovulation estimate.
Your Fertile Window
The fertile window spans 6 days: the 5 days before ovulation plus ovulation day itself. Sperm can survive in the reproductive tract for up to 5 days. The egg survives only 12–24 hours after release. Having intercourse in the 1–2 days immediately before ovulation gives the highest chance of conception.
Physical Signs of Approaching Ovulation
Cervical mucus changes are the most reliable physical sign. As ovulation approaches, mucus becomes clearer, stretchy and slippery — like raw egg white. This is your fertile-quality mucus and indicates peak fertility. After ovulation it becomes thicker and cloudy.
Basal body temperature (BBT) rises 0.2–0.5°C after ovulation and stays elevated until the next period. Taking BBT daily (before getting up) confirms ovulation has occurred — useful for pattern recognition over several cycles.
LH surge: Ovulation predictor kits (OPKs) detect the luteinising hormone surge that triggers ovulation 24–36 hours later. Testing daily around your predicted ovulation day gives advance warning.
Find your fertile window instantly with our ovulation calculator.
Use the Ovulation Calculator →