Pregnancy Week Calculator: Track Your Pregnancy Week by Week

Calculating pregnancy weeks is an essential step for every expecting mother. Whether you just found out you're pregnant or want to track your baby's development week by week, our online pregnancy calculator lets you know exactly where you stand. In just a few clicks, discover your number of weeks of amenorrhea (WA), gestational weeks (GW), your pregnancy month, trimester and most importantly, your estimated due date (EDD).

Why Is It Important to Know Your Pregnancy Progress?

Knowing exactly your number of pregnancy weeks is fundamental for several reasons. It's not just about satisfying curiosity: it's a real pregnancy tracking tool that directly impacts the health of both mother and baby.

Medical Follow-up and Prenatal Examinations

The pregnancy calendar is directly linked to the schedule of mandatory and recommended medical examinations. Each prenatal consultation is scheduled according to the number of weeks of amenorrhea:

• First ultrasound (dating scan): between weeks 11 and 13, to confirm the start date of pregnancy and check embryo vitality
• Second ultrasound (anatomy scan): between weeks 20 and 24, to examine the baby's morphology and organs in detail
• Third ultrasound (growth scan): between weeks 30 and 34, to check the baby's growth and position before delivery
• Monthly consultations: one visit per month from the 4th month of pregnancy

Baby Development Week by Week

Each week of pregnancy corresponds to a key stage in embryonic and fetal development:

Understanding the Difference Between Weeks of Amenorrhea and Gestational Weeks

Weeks of Amenorrhea (WA)

Weeks of amenorrhea are calculated from the first day of the last menstrual period. This is the method used by healthcare professionals because the date of the last period is generally known with precision. A pregnancy lasts approximately 40 weeks of amenorrhea (280 days).

Gestational Weeks (GW)

Gestational weeks are calculated from the presumed date of conception, approximately 14 days after the start of the last period. The pregnancy thus lasts about 38 gestational weeks. The formula is simple: GW = WA - 2.

How Is the Estimated Due Date (EDD) Calculated?

The estimated due date is calculated by adding 280 days (40 weeks) to the first day of the last menstrual period. This method, known as Naegele's rule, is the most commonly used by healthcare professionals.

It's important to note that the EDD is an estimate. Only 4-5% of babies are born on the exact due date. Most births occur between weeks 38 and 42.

Correspondence Table: Months, Weeks of Amenorrhea and Gestational Weeks

Month	Weeks of Amenorrhea (WA)	Gestational Weeks (GW)	Trimester
1st month	3 to 6 WA	1 to 4 GW	1st trimester
2nd month	7 to 10 WA	5 to 8 GW	1st trimester
3rd month	11 to 15 WA	9 to 13 GW	1st trimester
4th month	16 to 19 WA	14 to 17 GW	2nd trimester
5th month	20 to 24 WA	18 to 22 GW	2nd trimester
6th month	25 to 28 WA	23 to 26 GW	2nd trimester
7th month	29 to 32 WA	27 to 30 GW	3rd trimester
8th month	33 to 36 WA	31 to 34 GW	3rd trimester
9th month	37 to 41 WA	35 to 39 GW	3rd trimester

Frequently Asked Questions About Pregnancy Calculation

How do I know how many weeks pregnant I am?

To know how many weeks pregnant you are, simply count the number of days since the first day of your last menstrual period and divide by 7. This gives you the weeks of amenorrhea. For gestational weeks, subtract 2 weeks. Our calculator does this automatically.

What is the difference between WA and GW?

WA (weeks of amenorrhea) count from the first day of the last period, while GW (gestational weeks) count from the date of conception. There is always a 2-week gap: GW = WA - 2.

Is the estimated due date reliable?

The estimated due date (EDD) is based on an average pregnancy duration of 280 days. In reality, a delivery is considered full-term between 37 and 42 weeks. The EDD can be refined by the dating ultrasound performed in the first trimester.