What Is a Pregnancy Due Date Calculator?

By (embryologist) and (fertility counselor).
Last Update: 07/21/2015

A gestogram, pregnancy wheel or gestational disc is a very useful instrument that calculates how many weeks you are pregnant, the probable date of delivery (LMP), the weight and length of the fetus.

Provided below is an index with the 4 points we are going to expand on in this article.

It consists of two concentric wheels, on the outside there is a calendar with a circular shape that has the days and months of the year. Inside there are two other circles with the size and weight that the fetus normally has according to the week of pregnancy. In addition, some give other facts about the baby's development and growth.

The most complete gestograms give information about:

  • The estimated date of delivery (EDD).
  • Which weeks pregnant you are in.
  • Average fetal weight.
  • Average fetal size.
  • Biparietal diameter (BDP): the distance in millimeters between the parietal bones of the fetal head.
  • The length of the femur.

There are multiple gestational discs that you can find online and in smartphone applications.

How do I use a gestogram?

It's easy to use, and it's enough to know the start date of your last period before you get pregnant. Knowing this data, the arrow of the rotating wheel is placed on the day, and we will obtain the rest of information that gives us the calendar.

If you don't know the date of your last period, but you do know in which week of pregnancy you are, simply rotate the gestogram until the indicator with the text "TODAY" coincides with your current week of gestation.


The information is reliable and contrasted because the values that appear on the wheel are statistical data, obtained from the study of very large samples of individuals and in representative periods of time. What you do need to keep in mind is that they are average values, so the fetus does not necessarily have to measure the indicated size, it will simply give you a rough idea.

It is also important to pay attention to the parents when considering the baby's development. If the mother and father are of large constitution it is more likely that the baby presents the highest values of the gestogram or even exceeds them, the same would occur in the opposite case, if the parents are of small constitution, your child will be in the lowest values of the table. This does not mean that the child has a growth failure or is delayed, it will simply be a smaller newborn.

Pregnancy wheels are very informative and are an entertaining way to learn more about fetal development, but don't forget that they are averages of previous pregnancies and births. It will be in the gynecological revisions where, with the measurements obtained with the ultrasound, the obstetrician will indicate if they are within the normality.

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 Cristina Mestre Ferrer
Cristina Mestre Ferrer
B.Sc., M.Sc.
Bachelor's Degree in Biological Sciences, Genetics & Human Reproduction from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Embryologist at IVI Barcelona. More information about Cristina Mestre Ferrer
Adapted into english by:
 Sandra Fernández
Sandra Fernández
B.A., M.A.
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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