When do you ovulate?
Ovulation, the release of an egg from an ovary, happens about 14 days before the next period. The time from ovulation to the next period, the luteal phase, is fairly stable at 12 to 14 days, while the part of the cycle before ovulation varies. That is why someone with a 32-day cycle ovulates around day 18, not day 14.
The formulas
- Ovulation = first day of the last period + cycle length − luteal phase
- Fertile window = from 5 days before ovulation to 1 day after
- Next period = last period + cycle length
The fertile window lasts about 6 days because sperm can survive up to 5 days in the reproductive tract, while the egg lives only 12 to 24 hours.
Worked example
Your last period started on October 29, 2026, with a 28-day cycle and a 14-day luteal phase.
- Ovulation: October 29 + 28 − 14 days = November 12, 2026.
- Fertile window: November 7 to November 13.
- Next period expected on November 26; the following ovulation around December 10.
- If you conceive this cycle, the due date would be about August 5, 2027.
Chances of pregnancy by day
The chance of conceiving is highest when intercourse happens in the two days before ovulation and on the day itself. Studies of couples trying to conceive found the probability per cycle at its peak to be roughly 25 to 30% on the best days, and close to zero more than a day after ovulation.
Signs of ovulation
- Ovulation tests detect the LH surge 24 to 36 hours before ovulation.
- Cervical mucus becomes clear, slippery and stretchy, like raw egg white.
- Basal body temperature rises by about 0.5 °F (0.3 °C) after ovulation, confirming it has happened.
- Some people feel a brief pain on one side of the lower abdomen.
Irregular cycles
If your cycles vary by more than a few days, the calculator can only give a rough window. Track several cycles and use ovulation tests. Very irregular or absent cycles can point to conditions such as polycystic ovary syndrome, worth discussing with a doctor, especially if you have been trying to conceive for a year, or six months over age 35.
A note on medical advice
This calculator gives estimates based on averages. It does not replace advice from your doctor, midwife or health care provider, who will date your pregnancy and follow it with exams and ultrasounds.