Ovulation Calculator

Ovulation — the release of an egg from the ovary — typically occurs about 14 days before the next period starts, regardless of cycle length. This "luteal phase" is relatively constant at 12–16 days for most women. For a 28-day cycle, ovulation lands around day 14. For a 32-day cycle, it shifts to about day 18 (32 − 14). The fertile window spans roughly 5 days before ovulation through the day after, because sperm survive up to 5 days and the egg is viable for 12–24 hours.

Example with a 28-day cycle and LMP on March 1: next period expected March 29. Ovulation ≈ March 29 − 14 days = March 15. Fertile window ≈ March 10–16 (5 days before through 1 day after ovulation). For a 30-day cycle with LMP April 1: next period May 1, ovulation around April 17, fertile window April 12–18. Calendar methods work best when cycles are regular within 1–2 days month to month.

Irregular cycles reduce calendar accuracy. Body signs provide better real-time data: basal body temperature rises 0.2–0.5°C after ovulation; cervical mucus becomes clear and stretchy like egg whites near ovulation; ovulation predictor kits detect the LH surge 24–36 hours before egg release. Combining calendar estimates with these signs (symptothermal method) improves reliability for both conception and natural family planning.

Stress, illness, travel, and hormonal conditions like PCOS can delay or skip ovulation, shifting the fertile window unpredictably. A single negative month does not indicate infertility — clinical evaluation is usually considered after 12 months of trying (or 6 months if over 35). This calculator provides a starting estimate, not a guarantee of ovulation on a specific day.

Enter your last period start date and average cycle length to see predicted ovulation day, fertile window, and next expected period. Track several months of data to confirm whether your luteal phase consistently matches the 14-day assumption or needs personal adjustment.