Ovulation Calculator: How to Find Your Most Fertile Days

Your ovulation date is the single most important day in your cycle — whether you're trying to conceive, trying to avoid pregnancy, or simply want to understand your body better. Here's how to calculate it and what it actually means.

How Ovulation Works

Ovulation happens when one of your ovaries releases a mature egg. This typically occurs around the midpoint of your cycle. The egg travels down the fallopian tube and is available for fertilisation for just 12–24 hours.

The Simple Ovulation Calculation

For a regular cycle, ovulation typically occurs 14 days before your next expected period — not 14 days after your last period started (a common misconception).

So for a 28-day cycle: Ovulation ≈ Day 14
For a 32-day cycle: Ovulation ≈ Day 18
For a 24-day cycle: Ovulation ≈ Day 10

Your Fertile Window: The 6-Day Window

Sperm can survive in the reproductive tract for up to 5 days. This means your fertile window starts 5 days before ovulation and ends 1 day after. That's a 6-day window where pregnancy is possible.

The most fertile days are the 2 days before ovulation and ovulation day itself.

Signs You're Ovulating

• Cervical mucus changes — becomes clear and stretchy, like raw egg white
• Slight temperature rise — basal body temperature rises 0.2–0.5°C after ovulation
• Mild pelvic pain — some people feel a twinge on one side (mittelschmerz)
• Increased libido — hormones peak right before ovulation
• LH surge — detectable with ovulation test strips

How Luna Tracks Your Fertile Window

Luna calculates your ovulation date and fertile window automatically based on your cycle history. Your calendar shows a colour-coded fertile window in green, with your ovulation day highlighted. You can also log your BBT (basal body temperature) daily to cross-reference with Luna's predictions.

Start tracking your ovulation free with Luna →