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Gestational Age Calculator

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Estimated Date of Delivery
Gestational age

Gestational age is the number of weeks the pregnancy lasts or the age of the pregnancy. In other words, it is the number of weeks a baby has been in the uterus. It can also be termed as AOG and is calculated with the women’s last menstrual period and cycle length. Use this calculator, to find your gestational age.

The gestational age (AOG) usually lasts from 38 to 42 weeks. If a baby has born before 37 weeks, then it is said as premature.

What is Gestational Age

Gestational age is considered to be very important to know for every mother or parents. The period between conception and birth of the baby is called gestational time or age. This can be determined using a gestational age calculator. This period is measured by week and the development of a baby happens in this period.

Gestation age can be measured from the first day of the last menstrual period. Normally gestational age can be 38 to 42 weeks. Babies born before 37 weeks are known to be premature and babies born after 42 weeks are considered to be post-mature.

Methods of Calculating Gestational Age

There are various methods to determine the gestational age. Here are some common methods to determine it:

  • The most commonly used method is to calculate the gestational age from the first day of the last menstrual period. But this method is not reliable for those who don’t know their last period date.
  • Gestational age can be calculated from ovulation. Adding 14 days with ovulation can be a way to get the gestational age. It is not fully accurate, the difference of 2 to 3 days can be seen.
  • One of the most used methods to know the gestational age is to compare the gestational age calculated from obstetric ultrasound with the average gestational age of the same size baby calculated from the last menstrual period (LMP).

If the compared result of the baby’s gestational age with early obstetric ultrasound and last menstrual period differs, The age calculated from the early ultrasound will be used for the rest of the pregnancy. And this comparison also helps to determine if the baby is premature or postmature along with the size and weight comparison.

  • This one of the most used methods, in which gestational age can be calculated from Oocyte retrieval or Co-incubation. In the case of in vitro fertilization, you can add 14 days with con incubation to get the gestational age. This method is known to be very accurate.
  • You can use a gestational age calculator to know the gestational age of a bay. There are many calculators are available online sites and medical sites that you can use by adding small basic information that is required for knowing the gestational age of a baby.

Gestational Age Calculator

The gestational age calculator helps to know the gestational date of gestation age along with fertility window and probable ovulation. It helps to compare the development of the fetus calculated by a calculator with the average development from week to week. You can know the gestational age of the fetus, with putting some certain pieces of information.

How the gestational age calculator works

Commonly the gestational age calculators work based on some information about pregnancy and the menstrual cycle. The length of the menstrual cycle and the first day of the last period are used in the gestational calculator to know many dates which are very important to know while pregnant. Some of these dates are:

Estimated Due Date

This is one of the most important dates of the pregnancy. Parents of the baby get very curious to know the due date of the baby from the early stage of pregnancy. The due date can be calculated by entering the estimated conception date and the average duration of pregnancy 40 weeks.

Fertility Window

The fertility window is commonly estimated to be around the ovulation period. You can add 4 days before and after the ovulation period to know the Fertility window. Conception mostly occurs in this period.

Ovulation Date

You can calculate the estimated ovulation date with gestational age. The ovulation period is called the period around which ovulation occurs. To calculate your estimated due date and gestational age, enter the current date and the date your last menstrual period started. The gestational age is based on the date of the last period, not the date of conception. Because of this, a person is usually considered at least 4 weeks pregnant by the time they actually miss a period and have a positive pregnancy test. Gestational age estimates how far along you are in your pregnancy. Your health care provider uses the gestational age in weeks (rather than months) to plan your care during pregnancy. Most pregnancies last about 40 weeks from the first day of the last menstrual period. This calculator helps you estimate your date of delivery ("due date") based on the timing of your last menstrual period.

Estimated gestational age in weeks

You can know the development of the fetus week by week with the use of the gestational calculator. Monitoring the development of the baby is very important to know the status of the baby. Knowing the premature or post-mature status can be very helpful to change the estimated due date.

The Gestational Age of A Pregnancy

  • Most of the calculation of gestational age uses the first day of the last menstrual cycle and adds 14 days to know the conception date. The length of gestation age is calculated as 280 days from the last menstrual period and 266 days from conception.
  • There is another method by Naegele. In this method estimated due date can be calculated by adding 7 days with LMP and subtracting 3 months.
  • Gestational age calculation from the first day of the last period can differ in many cases. Such as taking a pill or having an irregular period. Women with irregular periods face problems about their dates and period of the menstrual cycle.
  • You can know the date of pregnancy by taking some physical exams. When in 12 weeks of the pregnancy you can feel the uterus coming over pubic-bone and it reaches the navel by the 20 weeks. The result of the exam is not always accurate, it can differ or many factors such as multiple pregnancy, and obesity, etc.
  • You can know the age of pregnancy with the Human Chorionic Gonadotropin blood test. This test is mostly done in 3 to 4 weeks to know the result as this test can give accurate results in the early weeks of pregnancy.
  • The most accurate method to know the gestation age, due-date age and pregnancy date is dating scans. The first ultrasound measurement of the fetus or embryo is called a dating scan. The dating scan is commonly done in 11 to 13 weeks of pregnancy. But in some exceptional cases, an early scan might be offered from 6 to 10 weeks.

The development of the fetus is the main focus of this scan. You can know many conditions with the help of this scan such as triplet, twin, etc. scan focuses on more detail of the baby with an increasing week to monitor the development and pinpoint any changes in estimated due date.


You can use the gestational age calculator to know the gestational age along with the due date and conception date. It helps to know the development of the fetus from week to week.

Pearls/Pitfalls: According to ACOG, ultrasound measurement in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.

Importend Notes and Disclaimer


Caveats and Recommendations: This calculator is NOT intended to diagnose illness or be used as a substitute for medical advice or treatment. Some models provide predictive outcomes which may not be accurate. Please consult a medical professional for any medical treatment or diagnosis advice.


Note: This calculator is presented for your own personal use and is to be used as a guide only. Medical and other decisions should NOT be based on the results of this calculator. Although this calculator has been tested, we cannot guarantee the accuracy of its calculations or results.


Disclaimer: This calculator is provided without warranty and CANNOT be used to diagnose or treat any disease or condition.

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