Ovulation Calculator

How ovulation day is calculated

Ovulation — the release of an egg from the ovary — usually occurs 14 days before the start of the next period, regardless of overall cycle length. This means that with a 28-day cycle, ovulation falls around day 14, while with a 35-day cycle it falls around day 21.

How to read the visual calendar

Below the calculation result, the calculator shows a visual calendar for two months — the current and the next — with color-coded highlights for key cycle days:

• Red days — estimated period days (current and next expected).
• Green days — the fertile window, when the chance of conception is highest.
• Highlighted dark day — ovulation day itself, the most likely moment of egg release.

This visual format is handy as a quick reference: just glance at the calendar to see which phase of the cycle you're currently in, without manually calculating dates.

What is the fertile window

The fertile window is the period when the chance of conception is highest. It includes the 5 days before ovulation plus ovulation day itself, since sperm can survive in a woman's body for up to 5 days waiting for an egg, while the egg itself only lives 12-24 hours after release.

Limitations of this method

This calculation is based on population averages and works best with a regular menstrual cycle. The actual ovulation day may differ from the calculated one due to stress, illness, weight changes, or other factors. For more precise ovulation detection, you can additionally use:

• Ovulation predictor kits — detect the luteinizing hormone (LH) surge in urine.
• Basal body temperature — a slight rise after ovulation.
• Cervical mucus — changes consistency on fertile days.

This calculator provides an estimate and is not a method of contraception or medical advice. For pregnancy planning or contraception, consult a doctor.