Use our ovulation calculator to determine your most fertile days

Ovulation Calculation

The beginning of the last cycle:

   Days of cycle

Ovulation and fertilisation take place around 14 days before expected menstrual bleeding. With irregular cycles, it can be difficult to determine the date of conception (fertilisation) and thus the gestational age (age of the unborn child) and the due date.


At the time of ovulation the cervical mucus becomes more fluid, allowing the rapid passage of sperm from the vagina into the uterus. After ovulation, the egg can be fertilised in the fallopian tube and settle in the womb. Since sperm has a lifespan of 3-4 days, sexual intercourse before ovulation can also lead to fertilisation even if the egg is not yet in the fallopian tube.

However, very few women can determine the exact date of ovulation. As such, the rule of thumb is: in a 28-day cycle, the best time for conception is between days 11 and 15. Where a couple has sexual intercourse every three days, they manage to “catch” the fertile days without having to calculate.

Girl or boy?

The probability of whether you will have a girl or a boy is influenced by the time of fertilisation Sperm carrying the female X chromosome have a longer lifespan than male sperm, while sperm with the male Y chromosome are faster than female sperm.
Having intercourse a few days before ovulation increases the chance of having a girl, as the longer lifespan of the female sperm is an advantage in this case. Where a couple has sexual intercourse around or shortly after ovulation, the faster male sperm increase their chance of having a boy.

Fertility dysfunction

Being underweight can affect fertility . Where the weight of a woman falls below a critical limit of 43 kg (or a BMI of below 18), she can expect irregular menstrual cycles or even the absence of ovulation and menstruation.


There may be a cycle where no ovulation occurs. The number of ovulations depends on age: a 20-year-old woman has an average of 10 ovulations per year, while a 40-year-old woman only has around 5 ovulations per year.

Please keep in mind: the ovulation calculator is not intended to be used as a method of contraception! The calculated data correspond to average values and may vary from woman to woman.


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