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Fertility Calculator

Determine your optimal fertility window over 3 cycles to better understand your most fertile days. Free and no sign-up required.

Fertility windows

What is the fertility window?

The fertility window is the period of your menstrual cycle during which pregnancy is possible. It lasts about 6 days: the 5 days before ovulation (because sperm can survive up to 5 days in the female reproductive tract) and the day of ovulation itself (the egg is only viable for 12 to 24 hours). Peak fertility occurs in the 2-3 days just before ovulation.

How this calculator determines your fertility

Our calculator estimates your ovulation date by subtracting 14 days from your total cycle length (because the luteal phase lasts an average of 14 days). From this date, it identifies the 6-day fertility window and repeats the calculation over several future cycles. This method, called the calendar method, is based on averages and works best for regular cycles.

Maximizing or planning conception

If you are trying to conceive, the most favorable days are the 2-3 days just before ovulation. Having intercourse every 1-2 days during this period optimizes the chances of fertilization. Complementing this approach with cervical mucus observation and possibly pharmacy ovulation tests allows more precise identification of the optimal timing.

Important warning

This calculator is an informational tool and should not be used as a contraception method. Ovulation can vary from cycle to cycle, even in women with regular cycles. For contraception, consult a healthcare professional who can recommend an appropriate method.

Frequently Asked Questions

When am I most fertile?
You are most fertile in the 5 days before ovulation and on the day of ovulation itself. Peak fertility occurs 2-3 days just before ovulation, when sperm can wait for the egg in the fallopian tubes.
How many days does the fertility window last?
The fertility window lasts about 6 days: 5 days before ovulation plus the day of ovulation. The 2-3 days directly before ovulation offer the best chances of conception.
How can I maximize my chances of getting pregnant?
Have intercourse every 1-2 days during your fertility window. Maintain a healthy lifestyle: balanced diet rich in folic acid, moderate physical activity, quality sleep. Avoid tobacco, alcohol and excessive stress.
Can you get pregnant outside the fertility window?
In theory no, because the egg only survives 12 to 24 hours after ovulation. However, ovulation can vary from cycle to cycle, making predictions imperfect. This calculator should therefore not be used as a contraceptive method.

Related Tools

Ovulation Calculator Cycle Calculator Due Date Calculator

This tool provides indicative estimates and should not be used as a contraception method. Consult a healthcare professional for any questions.

For complete tracking, download Rythia

Personalized AI predictions, daily briefings and tailored support for your menstrual cycle.

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