排卵日と妊娠可能期間を確認します。
Ovulation typically occurs 14 days before your next period — not 14 days after your last one. For a 28-day cycle: ovulation falls on day 14. For a 32-day cycle: ovulation falls on day 18 (32 − 14 = 18). The fertile window spans 5 days before ovulation plus the ovulation day itself, since sperm can survive up to 5 days in the reproductive tract.
How to use this calculator: Enter the first day of your last menstrual period (LMP) and your average cycle length. The calculator will show your estimated ovulation date, your fertile window, and when your next period is due.
Cycle lengths vary from 21 to 40 days and can change month to month due to stress, illness, travel, or hormonal changes. For the most reliable ovulation tracking, combine calendar calculation with basal body temperature (BBT) charting and ovulation predictor kits (OPKs), which detect the LH surge 24–36 hours before ovulation.