Online Gestational age Calculator: Calculate Estimated Date of Delivery (EDD)


Gestational age is the number of weeks the pregnancy lasts or the age of the pregnancy. Use this free Gestational age Calculator online, to find your gestational age. 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.

Last menstrual period
Cycle Length
Please, Enter all values correctly.
Estimated Date of Delivery
Gestational age


Calculating Gestational Age

Last Menstrual Period

If the woman has a normal cycle and knows the first day of her last menstrual period, it is possible to calculate the gestational age from that date. Gestational age is measured, not from the date of conception, from the first day of the last menstrual period of the mother.


The baby can be measured after the last menstrual period of the mother as early as 5 or 6 weeks. Measuring the baby with ultrasound in early pregnancy is most reliable. Later in pregnancy, it becomes less accurate. Between the 8th and 18th weeks of pregnancy, the best time to predict gestational age using ultrasound.

The most reliable way to determine gestational age is to use the first day of the last menstrual period of the female and verify this gestational age with the ultrasound test calculation.

Calculating Conception Date

In a Typical Pregnancy

Conception typically occurs between 11-21 days after the first day of the last period for a woman with a regular menstrual period. Most women don’t know the exact date of conception because knowing exactly when ovulation happens can be difficult. Thus, their date of conception is simply an estimate based on their last period’s first day.

Special Cases

Women performing special procedures, such as artificial insemination or in vitro fertilization, usually know the exact conception date.

Calculating Due Date:

Estimated Due Date

The estimated due date is 40 weeks from the first day of the year, depending on the last menstrual period. This is just an estimation since only about 5 percent of babies are born.

Difficulties in Determining the Gestational Age

Last Menstrual Period

It can be difficult to determine gestational age using this approach for women who have regular menstrual periods and women who can not recall the first day of their last menstrual period. In these situations, the determination of gestational age also involves an ultrasound test.

Baby’s Growth

Determining the gestational age is difficult in some situations because the child is exceptionally large or small. Also, in some cases, early pregnancy uterine size and later pregnancy uterine height does not suit the first day of the last menstrual period. It is also difficult to obtain a specific gestational age in these instances.


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Sharon Olabanji
Sharon Marie olabanji RN, CHO, Founder and CEO of Pregnancyvitamins, has a background in community health, nursing, and nutrition. As a mom of two, I do thorough research and I decide to take good care of my self and tackle health problems during pregnancy and after delivery. is the culmination of her thousands of hours of research and all posts are medically reviewed and verified by the research team.

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