Ovulation Calculator
Fertile window and ovulation date from your cycle.
An estimate. Cycles vary; this is not a contraceptive method.
How it works
Ovulation happens roughly one luteal phase before the next period, not a fixed number of days after the last one. The luteal phase is the more stable half of the cycle, usually 12-16 days, so counting backwards from the expected period is more reliable than counting forwards.
Sperm survive up to five days, the egg about 24 hours. That makes the fertile window the five days before ovulation plus the day itself.