Ovulation Calculator
Estimate when ovulation is likely and which days around it make up the fertile window, from the first day of your last period and your usual cycle length.
Estimate your fertile window
Frequently Asked Questions
By counting back 14 days from the next expected period, rather than forward from the last one. The luteal phase, between ovulation and the next period, is roughly 14 days whatever the cycle length, while the first half varies.
Roughly the five days before ovulation and the day of it. Sperm can survive several days in the reproductive tract, so intercourse before ovulation can still result in pregnancy.
No. Ovulation moves between cycles even for people with regular periods, and this calculation cannot see that. Fertility awareness methods that do work rely on daily measurements of temperature and cervical mucus, with training.
Then the estimate is weaker, because it starts from an assumption about a typical cycle. Ovulation predictor kits and basal temperature tracking observe what is actually happening.