Ovulation Tracker & Conception Window Calculator

Ovulation and Fertility Guide

The Fertile Window

An egg survives approximately 12–24 hours after ovulation. Sperm survive 3–5 days in fertile cervical mucus. This creates a fertile window of approximately 6 days — the 5 days before ovulation and the day of ovulation itself. The 2–3 days before ovulation and the day of ovulation are the most fertile days. For a 28-day cycle, ovulation typically occurs around day 14 (counting from the first day of the period). For a 35-day cycle, around day 21.

Calculating Ovulation Day

Ovulation day = cycle length − luteal phase length. The luteal phase (from ovulation to next period) is typically 12–16 days, most commonly 14 days. For a 28-day cycle: 28 − 14 = day 14. For a 35-day cycle: 35 − 14 = day 21. The luteal phase is relatively consistent for each person; the variability in cycle length usually comes from the follicular phase (period to ovulation). Tracking cycles for 3+ months gives a more accurate personal average.

Signs of Ovulation

Physiological signs: cervical mucus changes to clear, stretchy, egg-white consistency (most fertile) in the days before ovulation. Basal body temperature (BBT) rises by 0.2–0.4°C after ovulation and remains elevated. Ovulation predictor kits (OPKs) detect the LH surge that occurs 12–36 hours before ovulation — the most practical home method. Mittelschmerz (ovulation pain): mild one-sided pelvic pain lasting a few hours at ovulation, experienced by approximately 20% of women.

Important Limitations

This calculator provides a statistical estimate based on average cycle patterns. Actual ovulation can vary significantly due to illness, stress, travel, hormonal changes, and other factors. Women with irregular cycles (common with PCOS, thyroid conditions, perimenopause, and shortly after stopping hormonal contraception) may have unpredictable ovulation timing. For conception, monthly OPKs, BBT tracking, or both provide more accurate individual data than date-based calculations. For contraceptio