How to use the ovulation calculator
Enter the first day of your last period and your average cycle length. The calculator estimates your ovulation day, your most fertile window, and when your next period is likely to start. Everything is worked out in your browser and nothing you enter is stored.
Understanding the fertile window
Conception is most likely in the short window around ovulation. Because sperm can survive for several days inside the body, the fertile days begin a few days before the egg is released and end shortly after. Identifying this window is useful whether you are trying to conceive or simply want to understand your cycle better. The calculator marks the window so you can see the highest-probability days at a glance.
An estimate to guide, not a guarantee
Calendar-based predictions rely on averages, and real bodies vary. Ovulation can move earlier or later from one cycle to the next, and irregular cycles reduce accuracy further. Treat the dates here as a helpful guide and, if timing matters to you, combine them with direct signals like basal body temperature or ovulation predictor kits. This tool is for general information and is not medical advice or a method of contraception — for personal guidance, consult a healthcare professional.