Ovulation Calculator
Calculate your ovulation date and fertile window based on your last period and cycle length.
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How to use this calculator
- 1
Enter the first day of your most recent period (YYYY-MM-DD format).
- 2
Input your average cycle length — 28 days is typical but varies.
- 3
Leave luteal phase at 14 unless you know your specific luteal length.
- 4
Select how many months ahead you want predictions.
- 5
Your fertile window is highlighted — these are the days to try to conceive.
Frequently asked questions
When do I ovulate?
Ovulation typically occurs 14 days before your next period, not 14 days after your last period starts. So in a 28-day cycle, ovulation is around day 14. In a 35-day cycle, it's around day 21. The exact day varies and can shift due to stress, illness, or hormonal changes.
What is the fertile window?
The fertile window spans 5–6 days: the 5 days before ovulation and the day of ovulation itself. This is because sperm can survive up to 5 days in the reproductive tract, while the egg only survives 12–24 hours after release. Your highest chances of conception are 1–2 days before ovulation.
How accurate is this calculator?
This calculator provides estimates based on average cycle patterns. It assumes a regular cycle and a 14-day luteal phase. Cycles vary significantly due to stress, illness, weight changes, and hormonal conditions (PCOS, thyroid issues). For greater accuracy, use ovulation predictor kits (OPKs) or track basal body temperature (BBT).
What is the luteal phase?
The luteal phase is the second half of your cycle — from ovulation until your next period begins. It's typically 12–16 days (average 14). Unlike the first phase of your cycle (which varies), the luteal phase length is fairly consistent for each person. Knowing yours helps predict ovulation more accurately.
Free Ovulation Calculator — Find Your Fertile Days
How ovulation timing works
Your menstrual cycle has two phases separated by ovulation. The follicular phase (period start to ovulation) varies in length — this is why cycles of different lengths differ. The luteal phase (ovulation to next period) is nearly constant at around 14 days. To find your ovulation date: subtract 14 from your total cycle length. For a 32-day cycle: day 18 is ovulation. For a 26-day cycle: day 12 is ovulation.
Signs you're ovulating
Physical signs of ovulation include: (1) Cervical mucus changes — becomes clear, slippery, and egg-white-like. (2) Mittelschmerz — mild one-sided pelvic pain or cramping. (3) Basal body temperature (BBT) rise — a slight increase (0.2–0.5°C/0.4–0.9°F) after ovulation. (4) LH surge — detectable with an ovulation predictor kit 24–36 hours before ovulation. Tracking multiple signs improves accuracy.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →