How many weeks pregnant am I? How to calculate

Most women get confused about the number of days they have been in pregnancy, especially at the initial stages. It is natural to be excited and anxious to know and keep tabs on each moment of pregnancy. However, there is no way to know exactly when you ovulated and conceived.

This is also the reason even health professionals tend to date pregnancy based on their patient’s LMP (last menstrual period). Hence, it is very crucial to closely monitor your periods and keep a record of it if you have been planning for a baby.

Maintain a diary of your period so that you remember exactly when your last period started. So the first day of your LMP is counted as ‘Day One’ of your pregnancy. Thereafter, use this pregnancy calculator to find out your estimated due date.

Calculation of Due Date – How Many Weeks Pregnant are You?

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EDD (estimated date of delivery), also commonly referred to as the ‘due date’ is the expected date when you should actually start labor.

Since this date is simply an estimate, you may start labor anywhere between 2 weeks prior to or after the due date.

Indeed, only 1 in 20 pregnant ladies deliver exactly on the estimated due date. This is an indication that only 5 percent of babies across the globe are born on the exact calculated date.

Fetal Age vs. Gestational Age

The term ‘gestation’ is used for defining the time between actual conception date and birth or the time period a woman is pregnant (in weeks). Measurement of gestational age is done starting from the LMP to the present date in weeks.

Usually, pregnancies last anywhere between 38 and 42 weeks. In case, a baby is born before thirty seven weeks, he/she is considered a ‘preemie’ or premature.

Fetal Age is a different unit of measurement. It is done starting from the gestational age. The gestational age will measure a pregnancy span in weeks whereas Fetal Age is precisely the actual age of the growing baby.

First Day of Last Period

Most pregnancies tend to last around 40 weeks. Some last for 38 weeks from the date of conception. Hence, the best or most accurate way to estimate your due date is to count 40 weeks, or 280 days, starting from the first day of your last menstrual period (LMP).

Method 2

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There is another way to calculate pregnancy. You can subtract 3 months from the first day of your last period. Thereafter, you need to add 7 days to it.

This means if your last period started on April 08, you need to count back 3 months to January 08. Then add 7 days to it which will result as – January 15. This is precisely how your health care practitioner will estimate your due date.

PS: It is quite normal to deliver a week or two before or after.

Date of Conception

Women who have regular menstrual cycle can calculate their due date based on the first day of last period. On the other hand, if your cycle is not regular, this method will not work.

It is crucial to have a reliable estimated date of delivery (EDD). This is how you and your doctor can estimate your conception date. For estimated due date, you need to add 266 days to it.

Irregular Periods/Forgotten Date of Last Period

As already discussed, calculation for the due date works best if your menstrual cycle is regular. This means you need to get your periods every 28 days.

In case, you have an irregular menstrual cycle and you don’t know the date of your LMP, things may get a little difficult. Additionally, if your cycle varies in length, calculating from day 1 of your LMP may not give you an accurate date.

Ultrasound Scan

This is a good way out when you are unable to determine when you conceived. It also helps when you forget the day of your last menstrual period. An ultrasound can help you and your practitioner determine your due date.

An early ultrasound is important to calculate the due date. The test is recommended if periods are irregular or the patient is 35 years of age or older. Ultrasound is also a crucial step taken by health care practitioners if the patient has a history of miscarriages or complications in pregnancy.

Understanding a Trimester

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The literal meaning of “Trimester” is “3 months”. Most pregnancies last for 9 calendar months. Each pregnancy is categorized into 3 trimesters. This is a simple way to describe changes occurring inside a woman’s body.

  • First Trimester – It typically lasts from the beginning of your pregnancy until you are 13 weeks and 6 days pregnant.
  • Second Trimester – It lasts from 14 weeks to 27 weeks and 6 days of pregnancy. This is also known as the golden period where mother feels better, the bump starts showing, face glows and morning sickness fades off.
  • Third Trimester – The period lasts from 28 weeks of pregnancy until the baby comes out in this world.

How long does a standard pregnancy last?

Everything depends on the way you count it. A lot of people use this pregnancy calculator to determine their due date by counting forty weeks starting from the first day of their LMP.

Typically, forty weeks adds up to the following:

  • 9 calendar months (30 or 31 days each)


  • 10 lunar months (28 days each)

Final Note

The Meaning of ‘How Far along am I’

This is a phrase or an expression referring to the actual time passed during a woman’s pregnancy. This question is usually used to enquire about the number of weeks or months one is pregnant.

Length of Pregnancy

A pregnancy lasts for about 280 days (40 weeks). This period is counted starting from a woman’s last menstrual period.

How to tell how many weeks pregnant you are?

You can use a pregnancy calculator, ultrasound measurements, or count calendar days starting from the last period to the present time.

Information a calculator requires?

A typical calculator is based on the due date of a woman or last menstrual period (LMP).