Calculating the exact day on which a child was conceived or when it was conceived is not easy, as the duration of the menstrual cycle varies and the sperm can survive in the body for several days before fertilising the egg.

 

A normal pregnancy lasts 288 days. The average menstrual cycle is 28 days, with ovulation taking place 14 days before the onset of the period. A woman with a menstrual cycle of 28 days will therefore ovulate on day 14; with a menstrual cycle of 30 days on day 16. Day 1 is the first day of the period.

The calculation of fertilisation is therefore not based on the day on which sexual intercourse took place, but on the menstrual cycle and ovulation.

 

To find out the day of fertilisation, start by noting the day on which the period was expected. Then 14 days are subtracted from this date to calculate ovulation. It doesn't matter whether a woman has a 24, 28 or 30-day cycle, as ovulation always takes place 14 days before the first period. The day of ovulation is when fertilisation of the egg is most likely.