Ovulation Calculator

When do I ovulate?

Ovulation typically occurs about 14 days before your next period, not 14 days after your last period. This is because the luteal phase (the time between ovulation and your period) is consistently about 14 days long, while the follicular phase varies with cycle length. For a 28-day cycle, ovulation is around day 14. For a 35-day cycle, ovulation is around day 21.

What is a fertile window?

Your fertile window is the 6-day period when pregnancy is possible: the 5 days before ovulation plus the day of ovulation itself. Sperm can survive in the reproductive tract for up to 5 days, while an egg is viable for only 12–24 hours after release. The two days before ovulation and the day of ovulation are your most fertile days.

How accurate is an ovulation calculator?

Ovulation calculators provide estimates based on average cycle patterns. They work best for women with regular cycles (consistent cycle length within 1-2 days). For irregular cycles, ovulation predictor kits (OPKs) that detect the LH surge, basal body temperature charting, or cervical mucus monitoring provide more accurate predictions. Up to 30% of women have irregular cycles.

Can I get pregnant outside my fertile window?

Pregnancy is extremely unlikely outside the fertile window. However, if your cycles are irregular, your actual ovulation date may differ from the calculator estimate. Stress, illness, travel, and medication can shift ovulation by several days. If you are trying to avoid pregnancy, use this calculator as a guide only — not as contraception.

What is the implantation window?

The implantation window is the period 6 to 12 days after ovulation when a fertilized egg may attach to the uterine lining. Implantation typically occurs 8-10 days post-ovulation. Some women experience light spotting (implantation bleeding) during this time. A pregnancy test is most reliable after implantation is complete, approximately 12-14 days after ovulation.

What if my cycle is irregular?

If your cycle varies by more than 7 days from month to month, this calculator may be less accurate. For irregular cycles, consider tracking basal body temperature (BBT), cervical mucus changes, or using ovulation predictor kits (OPKs). Enter your average cycle length over the last 3-6 months for the best estimate. Cycles between 21-35 days are considered normal; outside this range, consult your healthcare provider.