Read this before using the Fertile window calculator: 

1. ​This calculator is for those women who want to know the dates when their chances of conceiving are higher in their period cycle.

2. Period cycle length is the difference between the starting days of two consecutive periods. In other words, it is the answer to the question when some one asks you after how many days your periods start again.

3. In order to use this calculator for better results, you need to know that your period has to be regular and has a fixed period cycle length. If there is a just a difference of 1-2 days delay or early, then it will be considered a regular periods only.​

4. This calculator will only give you the dates when your chances of conceiving are high. Whether you will conceive or not is something dependent on other factors too like the quality of eggs and sperm periods are regular or not, etc.