To independently determine the approximate due date, you can use a special pregnancy calculator or calculate the date using other specialized tools. However, to determine the due date, even approximately, you need to have certain information. How do you calculate the due date? We explain.
Due date and the date of the last menstrual period
One of the simplest methods for approximately determining the due date is to use the date of the last menstrual period. We can use this method to determine the due date ourselves or use tools such as, for example, a pregnancy calculator. If we have not yet confirmed the pregnancy with a doctor or do not know the exact date of conception, we can use the so-called Naegele's rule to calculate the approximate due date.
It assumes that the average cycle lasts 28 days, which is why the first day of pregnancy is considered to be the first day of the last menstrual period in this case. Therefore, if we remember the date of our last menstrual period, we can easily determine the approximate due date using special free pregnancy calculators available online. This rule works reasonably well only for women who have regular cycles because, according to Naegele's formula, the due date is the first day of the last menstrual period plus 7 days, minus 3 months, plus one year. However, if our cycle is irregular, then when using a pregnancy calculator based on Naegele's rule, in which we provide only the date of the last menstrual period, we must expect some inaccuracies.
Due date and the date of conception
Another way to determine the due date is to enter the exact date of conception into a pregnancy calculator. This is a good option for women who know the date when the baby was conceived. In this case, you can also use a pregnancy calculator based on Naegele's rule, and the due date calculated from this information may be more accurate than when you know only the date of the last menstrual period. However, it should be remembered that Naegele's rule used in free pregnancy calculators available online assumes that pregnancy lasts 280 days, or 40 weeks. Nevertheless, remember that our pregnancy may end both earlier and somewhat later.
Due date based on an ultrasound examination
Free pregnancy calculators available online allow you to quickly estimate the approximate due date based on the date of conception or the date of the last menstrual period. However, another, more accurate way to determine the due date may be an ultrasound examination. Usually, during the first visit to a gynecologist, the doctor assesses the size of the gestational sac or the baby's length, as well as the crown-rump length, and on this basis confirms the pregnancy and provides an approximate due date. Every pregnant woman should undergo an examination by a gynecologist, but especially women with irregular cycles may learn the approximate due date only during such a visit, because calculators are often ineffective in their case.