What Is a Pregnancy Due Date Calculator?

By BSc, MSc (embryologist) and BA, MA (fertility counselor).
Last Update: 08/17/2015

A pregnancy due date calculator, also known as pregnancy wheel or gestation calculator, is a very helpful tool that allows you to calculate how many weeks pregnant are you, the estimated delivery or due date (EDD or EDC), and the fetal length and weight.

The different sections of this article have been assembled into the following table of contents.

What is it about?

A pregnancy wheel is formed by two concentric wheels. The outer one contains a round-shaped calendar where the days and the months of the year are counted. Within the outer one, two more circles can be found. There you can find an average length and weight chart according to the stage of pregnancy you are in. Besides, there are even more accurate calculators where information about the baby’s development is shown as well.

Most accurate pregnancy wheels can provide you with the following information:

  • Estimated delivery or due date (EDD or EDC).
  • How many weeks pregnant are you.
  • Average fetal weight.
  • Average fetal length.
  • Biparietal diameter (BPD), i.e. the distance in millimeters between the parietal bones located in the fetus’ skull.
  • Fetal femur length.

There are many different types of pregnancy wheels available online and mobile apps designed to run on smartphones.

How does it work?

Its functioning is very simple. It is enough to know the date of your last menstruation before you got pregnant. Knowing this, the arrow of the wheel should point to this day and then we will be able to find out the rest of the information.

In case you forgot the date of your last period but you know in which week of pregnancy are you, then the only thing you have to do is rotating the pregnancy wheel towards the indicator that says “TODAY” so that it matches the current pregnancy week in which you are.


The information shown is accurate and reliable since all values appearing on it are based on statistical data. Such data have been obtained from the samples of different individuals in very representative periods of time. Nevertheless, you should bear in mind the fact that they are just average values, that is to say, fetal weight and length don’t have to necessarily be as indicated. All in all, this information gives us a rough view.

When it comes to monitoring the fetal development, it is important to focus on its parents as well. If both the mother and the father have a big body frame, the pregnancy wheel is more likely to show the highest values or even surpasse them. The same may occur the other way round: if the parents have a small body frame, then the wheel will point at the lowest values. It is important to bear in mind that this does not translate into a child’s growth deficit or retardation but just a smaller newborn.

Gestation calculators are very informative. Besides, they are an entertaining way through which more information about the fetal development can be obtained. However, it is important not to forget they are based on previous pregnancies and childbirths. Thus, gynecological examinations shouldn't be dismissed at any rate since it will be the obstetrician who will determine whether your baby's measurements are normal by means of an ultrasound scan.

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Authors and contributors

 Cristina Mestre Ferrer
Cristina Mestre Ferrer
BSc, MSc
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
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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