Methodology & Calculation

Transparency is key to trust in reproductive health tools. Our ovulation calculator is based on clinically recognized methods and established biological principles. Below, we explain exactly how your fertile days are determined.

1. The Knaus-Ogino Method

Our calculation follows the Knaus-Ogino method, also known as the calendar-based rhythm method. This method is grounded in the observation that while the first phase of the menstrual cycle (the follicular phase) can vary in length, the second phase (the luteal phase) is remarkably consistent at approximately 14 days.

2. The Calculation Formula

Key Variables Explained:

• LMP: The First Day of your Last Menstrual Period.
• Cycle Length: The average number of days from the start of one period to the start of the next.
• The 14-Day Constant: The estimated length of the luteal phase (time between ovulation and the next period).

The Fertile Window is calculated to be 6 days long. This accounts for the 5-day lifespan of sperm inside the female body and the 12-24 hour viability period of the egg once it has been released.

3. Scientific Reference Base

Our methodology aligns with data and guidelines provided by leading global health organizations, including the World Health Organization (WHO) and theNHS (UK). We focus on standardized mathematical models derived from large-scale epidemiological studies on female reproductive cycles.

4. Method Limitations

It is critical to note that the calendar method is an estimate. It is not suitable for women with highly irregular cycles or for those using it as a preventative (contraceptive) method. Individual cycles can shift by 2-3 days due to stress, dietary changes, or illness.