Ovulation Calculator
Find out when you're most likely to ovulate and identify your fertile window. Enter the first day of your last period and your average cycle length to see your estimated ovulation date and the best days for conception.
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How Is Ovulation Calculated?
Ovulation is estimated using the luteal phase method: the luteal phase (the time between ovulation and your next period) is relatively consistent at about 14 days for most people. So if your cycle is 28 days, ovulation likely occurs around day 14. For a 32-day cycle, it would be around day 18.
The fertile window includes the 5 days before ovulation and the day of ovulation itself. This is because sperm can survive in the reproductive tract for up to 5 days, while the egg is viable for only 12–24 hours after release. The most fertile days are typically the 2–3 days leading up to and including ovulation.
Signs of Ovulation
Many people experience physical signs around ovulation:
- Cervical mucus changes — Mucus becomes clear, slippery, and stretchy (like egg whites) near ovulation.
- Basal body temperature rise — A slight temperature increase (0.2–0.5°C) occurs after ovulation due to progesterone.
- Mittelschmerz — Mild pelvic pain or cramping on one side, caused by the egg being released.
- HRV changes — Heart rate variability often dips around ovulation, detectable by Apple Watch and used by Ovuly for smarter predictions.
Factors That Affect Ovulation Timing
Ovulation doesn't always happen on the same day. Stress, illness, travel, significant weight changes, and hormonal conditions like PCOS can all shift ovulation earlier or later in your cycle. Tracking biometric data — like wrist temperature and HRV — can help you detect ovulation more precisely than calendar methods alone.
Frequently Asked Questions
When do I ovulate?
Ovulation typically occurs about 14 days before your next period. For a 28-day cycle, that's around day 14. For a 30-day cycle, it's around day 16. The exact timing varies based on hormonal fluctuations and other factors.
How long does the fertile window last?
About 6 days — the 5 days before ovulation plus the day of ovulation itself. The egg survives 12–24 hours, but sperm can live up to 5 days.
What are the signs of ovulation?
Common signs include changes in cervical mucus (clear and stretchy), a slight temperature rise, mild pelvic pain, increased libido, and breast tenderness. Wearable data like HRV can also indicate ovulation.
Can I ovulate more than once per cycle?
You can release more than one egg during the same ovulation event (which causes fraternal twins), but you don't ovulate on two separate occasions in the same cycle.
Medical References
The information on this page is based on peer-reviewed medical sources. This tool is not a substitute for professional medical advice.
Want smarter predictions powered by your body?
Ovuly uses your Apple Watch data — HRV, wrist temperature, sleep — to make cycle predictions that go beyond calendar math.