Ovulation Calculator

First day of last menstrual period (LMP)

Average cycle length (days)

Calculate Ovulation

Ovulation typically occurs 14 days before the next period.

Ovulation Calculator — How It Works

This free ovulation calculator estimates your ovulation date, fertile window, and next period based on the first day of your last menstrual period and your average cycle length.

Ovulation formula

• Ovulation day = Cycle length − 14 days (luteal phase is typically 14 days)
• Fertile window = Ovulation day − 5 days to ovulation day + 1 day
• Next period = LMP + cycle length

Fertile window explanation

Sperm can survive in the female reproductive tract for up to 5 days. An egg survives for approximately 12–24 hours after ovulation. Therefore, the fertile window spans roughly 6 days: the 5 days before ovulation and the day of ovulation itself.

Signs of ovulation

• Cervical mucus change: becomes clear, slippery, egg-white consistency
• Basal body temperature (BBT): slight rise of 0.2–0.5°C after ovulation
• LH surge: detected by ovulation predictor kits (OPKs) 12–36 hours before ovulation
• Mittelschmerz: mild one-sided pelvic pain at time of ovulation
• Breast tenderness, increased libido

Tips for conception

• Have intercourse every 1–2 days during the fertile window for best results
• Track multiple cycles to identify your personal pattern
• Use OPKs or BBT monitoring for greater precision
• Maintain a healthy BMI, diet, and lifestyle

References

• Wilcox AJ et al. (1995). "Timing of sexual intercourse in relation to ovulation." NEJM 333(23):1517–1521.
• Stanford JB & Mikolajczyk RT (2002). "Methodological review of the fertile window." Am J Obstet Gynecol 187(5):1184–1192.
• ACOG. "Fertility Awareness-Based Methods of Family Planning." Practice Bulletin.