Pregnancy Calculator: How to Calculate Pregnancy Due Date Week By Week

Stages in Pregnancy Until 8 Months Pregnant

The estimated due date (EDD or EDC) is the date that the spontaneous onset of labor is expected to happen. The due date may be evaluated by adding 280 days (9 months and 7 days) to the first day of the last menstrual period (LMP). This is the method used by “pregnancy wheels”.

The accuracy of the EDD derived from this technique relies on upon exact recall by the mother, expect a regular 28 days cycle, and that conception happens on day 14 of the cycle. Use of the LMP to establish the due date may overestimate the duration of the pregnancy, and can be answerable to an error of more than 2 weeks.

Pregnancy Due Date and Gestational Age Calculator

The PDD is a tool mothers use to calculate the conception date (date of ovulation, egg retrieval, or insemination). It is a useful used by millions of expectant mother like you around the world.

The tool is also useful in date of 3-day embryo transfer, date of 5-day embryo transfer, the due date by sonogram (reverse calculation), and the first day of last menstrual period. In order to use this tool, visit perinatoloy and make a selection from the list as seen below, select the month, date, year and click calculate to get your results.

As you can see, the PPD on the screen below gives you the full results including the details of your next doctor’s visit and the required screening before the baby’s due date.


In cases where the date of conception is known accurately, for example, such as in vitro treatment, the EDD is calculated by adding 266 days to the date of conception.

Ultrasound uses the size of the focus to determine the gestational age (the time elapsed since the first day of the last menstrual period). The accuracy of the ultrasound calculation of the gestational age varies as indicated by the gestational age.

“Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate system to establish or affirm gestational age”

The American College of Obstetricians and Gynecologists recommends that ultrasound-established dates should take preference over menstrual dates when the discrepancy between ultrasound dating and LMP is

  • Greater than 5 days before 9 0/7 weeks of gestation
  • Greater than 7 days from 9 0/7 weeks to 15 6/7 weeks
  • Greater than 10 days from 16 0/7 weeks to 21 6/7 weeks
  • Greater than 14 days from 22 0/7 weeks to 27 6/7 weeks
  • Greater than 21 days after 28 0/7 weeks.

“Because of the risk of redating a small fetus that may be growth restricted, management decisions based on third-trimester ultrasonography alone are especially problematic; they need to be guided by careful consideration of the entire clinical picture and may require closer surveillance, including repeat ultrasonography to ensure appropriate interval growth.”

In Case Pregnancy Calculator Indicates Twins

At the point twin pregnancy is the result of in vitro fertilization determination of gestational age should be produced from the date of embryo transfer. Else, date the pregnancy using the larger embryo.

Different Methods For Estimating the Gestational Age during Pregnancy

Clinical Examination

A pelvic examination supported by good menstrual records in the first trimester has been reported to be a dependable system for dating of pregnancy.

Doppler Ultrasonography

The fetal heart can be heard using Doppler ultrasound by 10 to 12 weeks in most patients [10]. The gestational age should, therefore, be no less than 10 to 12 weeks if the fetal heart tones are heard.

Human Chorionic Gonadotropin Pregnancy Test

Human chorionic gonadotropin first becomes detectable in the mother’s blood and urine around 6 and 14 days after fertilizations (3 to 4 weeks gestational age) [11-13]. The gestational age would, thus, be at least 3 to 4 weeks at the time of a liable hCG pregnancy test.

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