Ovulation & Cycle Calculator

The calculator uses the calendar method: it adds the cycle length minus the luteal phase to the first day of your last period. For a 28-day cycle with a 14-day luteal phase, ovulation therefore falls roughly 14 days after the period begins. Ovulation is always shown for the next cycle that lies today or in the future.

No. The calendar method is NOT a reliable method of contraception. Its failure rate is around 15–24% per year, because cycles vary individually and ovulation can shift. For preventing pregnancy, reliable methods such as the pill, IUD or condom are far more suitable. Talk to your doctor about this.

The fertile days are the five days before ovulation, ovulation day itself and the day after. This is because sperm can survive in the female body for up to five days, while the egg is only able to be fertilised for about 24 hours. The highest chance of conception is on the one to two days immediately before ovulation.

The calendar method assumes a constant cycle length. If your cycle varies a lot, ovulation shifts too and the prediction becomes less accurate. In that case, methods that measure body signals — such as the symptothermal method with basal body temperature and cervical mucus — give far more reliable indications of actual ovulation.

No. The entire calculation runs directly in your browser. Your cycle and reproductive data — specially protected under Art. 9 GDPR — is never sent to a server, stored or analysed. If you share your result via a link, the values are only in that address and nowhere else.