Ovulation Calculator
Find your fertile window and ovulation day from your last period and cycle length.
PregnancyScience-backed formula
Enter your details
Fill in the fields, then calculate
Please choose a date.
Enter your cycle length.
Awaiting Data
Enter your details and tap Calculate to see your results appear here.
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ResultYour result appears here.
What Ovulation Means
Ovulation is when an ovary releases an egg. It is the most fertile point of your cycle and usually falls about 14 days before your next period.
Key dates line up into an easy week by week timeline.
The fertile window spans the five days before ovulation plus the day itself, since sperm can survive that long.
Cycle length shifts the timing, so the tool adjusts for it.
How to Use This Calculator
- Choose the first day of your last period.
- Set your cycle length.
- Tap Calculate for ovulation and your fertile window.
The Formula Used
Ovulation ≈ last period + (cycle − 14)
Fertile window = ovulation − 5 days to ovulation + 1
Fertile window = ovulation − 5 days to ovulation + 1
- cycle
- Days from one period to the next.
Understanding Your Results
Window opens
5 days before ovulation
Conception becomes possible.
Peak fertility
1 to 2 days before
The highest chance.
Window closes
1 day after ovulation
The egg's lifespan ends.
Tips to Improve
- Track cycles for a few months to learn your pattern.
- Watch cervical mucus and basal temperature.
- Ovulation kits confirm the surge.
- See a provider if cycles are very irregular.
Frequently Asked Questions
The two days before ovulation and the day itself offer the best chance.
No. It depends on cycle length and falls about 14 days before the next period.
Ovulation predictor kits, temperature charting, and mucus changes all help.
Scientific References
- Wilcox, A. J., et al. (1995). Timing of intercourse in relation to ovulation. NEJM, 333(23), 1517–1521.
- Ecochard, R., et al. (2001). Use of urinary markers to detect ovulation. Fertility and Sterility, 76(4), 678–683.
- American Society for Reproductive Medicine. (2017). Optimizing natural fertility.