The Fertile Window Calculator estimates the days in your menstrual cycle when you are most likely to conceive. It calculates your ovulation day (when an egg is released from the ovary) and identifies the fertile window, which usually spans five days before ovulation and one day after. This period is when sperm and egg have the highest chance of meeting, making conception more likely. By entering the first day of your last period and your average cycle length, this calculator helps you understand your reproductive pattern, plan for pregnancy, or manage natural family planning more effectively.