Gestational Age Calculator: How Many Weeks Pregnant Am I?

Updated in November 2023
Scientifically proven

To calculate your gestational age, or many weeks pregnant you are, you need to know the date of your Last Menstrual Period (LMP). Starting from this date, count the weeks up to today's date. This number will correspond to the number of weeks pregnant.

For example, if the current date was June 23, a woman who had her first period on April 15 should count of 9 weeks plus 6 days between the two dates. 

The doctor can also tell you the corrected gestational age, which is the date suggested by an ultrasound. This date is considered to be more accurate and helps to predict the probable date of delivery. Check out our online due date calculator to determine the possible delivery date. 

Online gestational age calculator

The easiest way to find out your gestational age is to use our gestational age calculator:

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This calculator helps you find out the number of weeks and days that have passed since the start of your pregnancy simply by entering the date of your last period.

What if I don't know the date of my last period?

If you're not sure when your last period was, the most accurate way to find out how many weeks pregnant you are is to consult your obstetrician, who will be able to tell you your gestational age via ultrasound.

Gestational age in weeks and months

This following table classigies your gestational age by weeks and months:

Trimester Month Weeks Included
1st trimester 1 month up to 4 and a half weeks of pregnancy
1st trimester 2 months

4 and a half weeks to 9 weeks

1st trimester 3 months

10 to 13 and a half  weeks of pregnancy

2nd trimester 4 months

13 and a half  weeks to 18 weeks of pregnancy

2nd trimester 5 months

19 to 22 and a half weeks  of pregnancy

2nd trimester 6 months

23 to 27 weeks of pregnancy

3rd trimester 7 months

28 to 31 and a half weeks of pregnancy

3rd trimester 8 months

32 to 36 weeks of pregnancy

3rd trimester 9 months

37 to 42 weeks of pregnancy

Usually a pregnancy lasts 40 weeks, but the baby can be born between 39 and 41 weeks without any concerns. If labor does not start spontaneously until the 41-week mark, the doctor may choose to induce labor with IV oxytocin.

How to calculate the estimated due date

To calculate your estimated due date, which should be around 40 weeks after your LMD, add 7 days to your LMD, and then count 3 months back and add one year.

For example, if the LMD was March 11, 2021, add 7 days, (March 18, 2021), then subtract 3 months (December 18, 2020) and add 1 year (December 18, 2021). In this case, the estimated due date is December 18, 2018.

This calculation is not 100% accurate, as the baby can be born between 37 and 42 weeks of pregnancy, however, it allows the parents and health care team to prepare for delivery.