Ovulation Calculator — Fertile Window Tracker

Enter your last period date and cycle length to instantly calculate your ovulation day, most fertile days and next period date.

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What Is Ovulation?

Ovulation is the release of a mature egg from the ovary. In an average 28-day cycle it occurs around day 14. The egg lives 12–24 hours; sperm can survive 3–5 days. The 5 days before ovulation plus ovulation day form the fertile window.

How It's Calculated

Ovulation = LMP + (Cycle - 14 days)\nFertile Window = Ovulation - 5 days to +1 day\nNext Period = LMP + Cycle length

How to use?

  1. 1
    Enter your datesSelect the first day of your last menstrual period. Adjust cycle length (default 28) and period duration (default 5) if needed.
  2. 2
    Click CalculateThe tool instantly shows your ovulation day, fertile window start and end, and estimated next period date.
  3. 3
    Plan accordinglyUse the fertile window to time intercourse for conception, or copy and share the results with your doctor.

FAQ

How long does the fertile window last?
The fertile window is typically 6 days: the 5 days before ovulation and ovulation day itself. Sperm can survive up to 5 days, and the egg lives up to 24 hours. Peak fertility is 1–2 days before ovulation.
Can I use this with irregular periods?
This tool is calibrated for regular cycles of 21–35 days. If your cycle is irregular, try entering your average cycle length from the past 3 months. For precise planning, consult a gynaecologist.
What are the signs of ovulation?
Common signs: egg-white cervical mucus, a 0.2–0.5 °C rise in basal body temperature, mild one-sided pelvic pain (Mittelschmerz), light spotting, and a positive LH surge on an OPK test strip.

How Does the Ovulation Calculator Work?

Our free ovulation calculator uses the standard Naegele-based formula: ovulation typically occurs 14 days before the next period. Enter your last menstrual period (LMP) date and average cycle length to get your ovulation day, 7-day fertile window, and next expected period.

When Is the Fertile Window?

An egg survives 12–24 hours after release, but sperm can live up to 5 days in the reproductive tract. This means the fertile window spans 5 days before ovulation through 1 day after—a total of 7 days. Pregnancy is most likely in the 1–2 days before and on the day of ovulation.

Signs of Ovulation

Common ovulation signs include: egg-white cervical mucus, a slight rise in basal body temperature (0.2–0.5 °C), mild pelvic pain (Mittelschmerz), and a positive LH surge on an ovulation test strip.

Disclaimer

Results are estimates only. Do not use this tool as a method of contraception or as a substitute for professional medical advice.

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