Date of conception: how to calculate the day I got pregnant

Conception is the moment when the sperm manages to fertilize the egg, starting the gestation process.

Although it is an easy moment to explain, trying to find out what day conception occurred is quite difficult, as the woman normally does not feel any symptoms and may have had unprotected sex on different days close to conception.

Thus, the conception date is calculated as an interval of 10 days, which represents the period in which the egg fertilization must have occurred.

There are three main ways to calculate the conception period:

1. Through the last menstruation

To find out which days you could have become pregnant, enter the date of the first day of your last period:

It is important to bear in mind that this calculator is more accurate for women who have a regular 28-day cycle. It is recommended that other methods be used to calculate the conception period if the cycle is shorter, longer or irregular.

Conception usually happens 11 to 21 days after the first day of your last menstrual period. Thus, if a woman knows the first day of her last menstrual period, she can estimate a period of 10 days in which conception could have occurred. To do this, simply add 11 and 21 days to the first day of your last menstrual period.

For example, if the last menstrual period appeared on March 5th, it means that conception must have occurred between March 16th and 26th.

Make an appointment with your nearest obstetrician, using the following tool, to better understand how to know your conception date:

2. Using the estimated birth date

This technique is similar to calculating the date of the last menstruation and is used, especially, by women who do not remember when the first day of their last menstruation was. Thus, using the date estimated by the doctor for delivery, it is possible to find out when the first day of the last menstruation might have been and, then, calculate the time interval for conception.

Generally, The doctor estimates delivery for 40 weeks after the first day of the last menstrual period and, therefore, if you remove those 40 weeks from the expected date of delivery, you are left with the date of the first day of the last menstrual period before pregnancy. With this information, it is then possible to calculate the 10-day period for conception, adding 11 to 21 days to that date.

Thus, in the case of a woman with an expected birth date of November 10th, for example, 40 weeks must be removed to find the possible first day of the last menstrual period, which, in this case, will be February 3rd. To that day, we must now add the 11th and 21st days to discover the 10-day interval for conception, which must then have been between the 14th and 24th of February

3. Through gestational age

To know the date of conception from the gestational age, it is necessary to count backwards. In other words, in the case of being 20 weeks pregnant on November 15th, for example, by subtracting 20 weeks, it is possible to verify that the date of the last menstruation was on June 28th.