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Ovulation Calculator

Predict your ovulation day, fertile window and next periods for the coming cycles, and the due date if you conceive.

Formulas last reviewed: September 2026

Disclaimer: Results are general estimates for information and education only. They are not medical advice, a diagnosis or a treatment plan. Please talk to a doctor or qualified health professional before making health, diet, exercise or pregnancy decisions.

What is ovulation?

Ovulation is when an ovary releases an egg. The egg survives only about 12 to 24 hours, but sperm can live up to 5 days — so the fertile window is roughly the five days before ovulation and the day itself.

This calculator predicts your ovulation day, fertile window and next periods for six cycles, and the due date if you conceive that cycle.

How it is calculated

Ovulation = first day of last period + (cycle length − 14 days)
Fertile window = 5 days before ovulation to 1 day after

The 14 days after ovulation (the luteal phase) is fairly constant, so a longer or shorter cycle changes when ovulation happens.

Worked example

Last period 1 January, 28-day cycle

Ovulation
Thu, 15 Jan 2026
Fertile window
10 Jan – 16 Jan 2026
Next period
Thu, 29 Jan 2026
Due date if conceived
Thu, 8 Oct 2026

Signs that ovulation is near

  • Clear, stretchy cervical mucus like raw egg white.
  • A small rise in basal body temperature (about 0.3–0.5 °C) after ovulation.
  • Mild one-sided pelvic pain or increased libido.
  • A positive ovulation predictor (LH) test 12 to 36 hours before ovulation.

Calendar predictions are estimates. Stress, illness and travel can move ovulation. Ovulation kits or tracking give more precise timing.

Frequently asked questions

Can I get pregnant on any day of my cycle?

Pregnancy is possible only in the fertile window, but cycles vary, so predictions are not a reliable way to avoid pregnancy.

How do I calculate ovulation with an irregular cycle?

Calendar methods are less reliable. Track cervical mucus, basal temperature or use LH strips over several cycles, and speak to a doctor if cycles are very irregular.

How long is the luteal phase?

Usually 12 to 14 days. You can change it in the calculator if you know yours.

When should I take a pregnancy test?

From the first day of a missed period, or about 14 days after ovulation, for the most reliable result.