Ovulation Calculator

Enter your last period start date and cycle length, and the calculator subtracts a fixed 14-day luteal phase from your cycle to place ovulation at day (cycle length - 14). For a 28-day cycle that puts ovulation on day 14. The fertile window runs from 5 days before ovulation through 1 day after, giving you a 6-day window in total.

If your cycles are regular, the predicted window is a reasonable starting point, but the fixed 14-day luteal phase is an average and your real luteal phase may differ. Stress, illness, travel, and hormonal changes can shift actual ovulation by several days. Treat the output as an estimate, not a diagnosis. For fertility concerns or trouble conceiving, talk to a clinician.

Most adults have cycles between 21 and 35 days, with 28 days being the classic textbook number. The calculator accepts any cycle from 20 to 45 days. A few days of variation between cycles is normal; persistent irregularity outside that range is worth discussing with a doctor.

See a doctor if your cycles are shorter than 21 days or longer than 35 days, vary by more than 7 to 9 days between cycles, or you have been trying to conceive for 12 months (or 6 months if you are over 35). Abnormal bleeding or sudden changes in cycle pattern are also worth raising promptly.

No. Ovulation day is when the egg is released, and the egg survives only 12 to 24 hours. But sperm can live up to 5 days in fertile cervical mucus, so the 5 days before ovulation plus ovulation day itself are all viable for conception. The calculator marks ovulation day plus 1 day after as the end of the window to account for the brief egg lifespan.