Pregnancy 101: How Many Weeks Pregnant Am I?

If you are or you think you might be pregnant, it is worth celebrating but it is rather confusing to know how many weeks you are already pregnant. This is because the weeks of your pregnancy are often calculated by doctors and midwives with 40 weeks being your expected date of delivery.


Medical professionals usually discuss pregnancies in terms of weeks instead of months because this is the closest to accurate evaluation of pregnancy progress and milestones that your pregnancy should experience.


On the average, pregnancies are expected to complete a total of 40 weeks or 280 days which is calculated from your last menstrual period – medically shortened to LMP.


Also, pregnancy is often equated to gestational age instead of fetal age development. Looking at this closely, the average gestational age is only 38 weeks after fertilization so this means you are two weeks pregnant during ovulation.


If you want to know how many weeks pregnant you are using the classic system, you can just count the weeks after your last menstrual period.


Fetal Age System: How many weeks pregnant am I?


There are times when medical professionals would talk in terms of fetal age or the ovulation system to determine the age of pregnancy in weeks since it is more precise than guessing you ovulated 14 days after the first day of your LMP.


Fetal aging system determines the actual age of the baby – the number of weeks since fertilization.


Technological advancements like ultrasound made it possible to accurately test ovulation and determine fetal age easily so a better estimation of the number of weeks is achieved.


If you have shorter or longer cycle than the average 28 days, the standard gestational age system cannot match where your baby needs to be so fetal age will prove to be more accurate.




There are three trimesters for pregnancy occurring 12 weeks each. The three trimesters will represent the various stages of pregnancy in terms of what is expected women are going to experience and the progress of the baby.


How far along am I will my pregnancy last?


The primary reason why women want to know the number of weeks they are pregnant is because they want to know how long they will still carry the baby.


Naegele’s rule is the traditional way of estimating delivery dates. This rule states that you need to add seven days to the first day of LMP and calculate nine months after the month of LMP.


Example: First day of LMP is November 18. Add 7 days to this date so it becomes 24. Count 9 months from November so you will arrive at EDD of August 24.


The rule assumes that a woman has the regular 28-day cycle.


However, despite the simplicity of this calculation only 3-5% of babies are born on their expected due date, which is often frustrating.


Commonly, babies are born at 40 weeks and 3 days. Statistically speaking, overdue is more common than early delivery.


Many professionals would claim that babies can be born healthy anywhere from 37 to 42 weeks after their LMP. In fact, more than 90% of babies are being born between 37 and 41 weeks of gestation. About 8% of babies are premature – born before 37 weeks of gestation and only 0.5% of babies are born before 32 weeks.