Ovulation Window Calculator

Calculate your fertile window and estimated ovulation date from your last period and average cycle length.

First day of last period

Average cycle length (days)

About Ovulation Window

Ovulation typically occurs 14 days before the next period (luteal phase is relatively constant at ~14 days). The fertile window spans 5 days before ovulation plus the ovulation day itself — the egg survives ~24h but sperm can survive up to 5 days. The LH surge occurs 24–36 hours before ovulation and is detected by OPK tests.