Fertility Window Calculator

Estimate your most fertile days based on menstrual cycle length. This tool is designed for educational and planning purposes only.

Calculate Your Fertility Window

First day of last period Average cycle length (days)

Your fertile window will appear here.

What is a Fertility Window?

The fertility window is the time during a menstrual cycle when pregnancy is most likely. It typically includes the five days before ovulation and the day of ovulation itself.

Why Use a Fertility Window Calculator?

✔ Helps understand menstrual cycle patterns
✔ Useful for family planning awareness
✔ Simple estimation without medical devices
✔ Fast and private calculation

Calculator Stats

Inputs: Last period date, average cycle length
Outputs: Estimated ovulation & fertile days
Method: Calendar-based estimation

Calculation Formula (Estimation)

Ovulation is estimated as:

Ovulation Day = Cycle Length − 14

Fertile window includes:

Ovulation Day − 5 through Ovulation Day