About the ovulation calculator
Ovulation usually happens about 14 days before your next period starts. The fertile window is the six days ending on ovulation day, because sperm can live up to five days and the egg survives about 24 hours.
If your cycles are irregular, this estimate is less reliable. Tracking basal body temperature, cervical mucus or using ovulation tests gives a better signal.
Formula
Ovulation day = cycle start + (cycle length − luteal phase). Fertile window = 5 days before ovulation through 1 day after.
Frequently asked questions
When am I most fertile?
The two days before and the day of ovulation have the highest chance of conception.
Can I rely on this to avoid pregnancy?
No. Calendar predictions are not a reliable form of birth control, especially with irregular cycles.
These calculators give general estimates and are not medical advice. Talk to a doctor or registered dietitian before changing your diet or exercise routine.