Ovulation Calculator

The calculator places ovulation 14 days before your next expected period. For a 28-day cycle that means day 14; for a 32-day cycle it means day 18. This is based on the standard assumption that the luteal phase (post-ovulation) is consistently about 14 days, while the follicular phase length varies between individuals.

The fertile window is the period during which intercourse can result in pregnancy. It spans the 5 days before ovulation (due to sperm surviving up to 5 days in the reproductive tract) plus the day of ovulation and the day after (the egg is viable for 12–24 hours). This calculator highlights all 7 days.

The prediction assumes a regular cycle and a fixed 14-day luteal phase. For women with irregular cycles, stress, illness, or hormonal changes, actual ovulation can shift by several days. For precision fertility planning, confirm ovulation with ovulation predictor kits (OPKs) or basal body temperature (BBT) charting.

Enter your average cycle length in days, measured from the first day of one period to the first day of the next. If your cycles vary, use the average of your last three to six cycles. The calculator accepts values between 21 and 35 days; inputs outside this range are considered outside the typical clinical norm.

You can, but the results will be less reliable. If your cycle varies by more than a few days each month, the calendar-based method is less precise. Consider using additional tracking methods such as OPKs, BBT monitoring, or consulting a healthcare provider for personalized guidance.

The forecast table projects your estimated fertile window, ovulation day, and next period start for each of the next 6 cycles, calculated by repeatedly adding your cycle length to the starting date. This lets you plan appointments, travel, or conception attempts well in advance.

All dates are computed as calendar dates in your local time zone using the browser's Date API with a T00:00:00 suffix to avoid UTC offset issues. The day-of-week label shown in results uses the en-US locale short format (e.g., Mon, Jan 6, 2025).

No. This calculator is an educational tool based on average cycle assumptions. For fertility treatment, reproductive health concerns, or contraceptive planning, please consult a licensed gynecologist or reproductive endocrinologist.