To calculate your gestational age, ormany 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:
This calculator helps you find out the number of weeks and days that have passed since the start of your pregnancysimply 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 classifiesyourgestational age by weeks andmonths:
| 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 weeksto9 weeks |
| 1st trimester | 3 months | 10 to 13 and a half weeks of pregnancy |
| 2nd trimester | 4 months | 13 and a half weeksto 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 the41-week mark, the doctor may choose to induce labor with IV oxytocin.
How to calculate the estimated due date
To calculate your estimateddue 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 subtract3 months (December 18, 2020) and add1 year (December 18, 2021). In this case, the estimated due date isDecember 18, 2018.
This calculation is not 100% accurate, asthe baby can be born between 37 and 42 weeks of pregnancy, however, it allows the parents and health care team to prepare for delivery.
Clinical review:
Dr. Marcelo Nunes
Obstetrician and Gynecology
Medical coordinator of Emergency Gynecology and Obstetrics at Rede D'Or - Itaim and Maternidade Star Units. CRM 116866-SP.
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Update History
We regularly update our content with the latest scientific information to maintain an exceptional level of quality.
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12 April, 2024 (Current version)
Updated by Daisy Oliveira - Registered Nurse
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13 November, 2023
Updated by Daisy Oliveira - Registered Nurse
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10 November, 2022
Updated by Manuel Reis - Registered Nurse
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14 July, 2022
Updated by Manuel Reis - Registered Nurse
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16 November, 2018
Clinical review by Dr. Marcelo Nunes - Obstetrician and Gynecology
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Published in November, 2018
References
- HALL, Eric S. et al. Evaluation of Gestational Age Estimate Method on the Calculation of Preterm Birth Rates. Matern Child Health J. 2013
- PEREIRA, Ana Paula E. et al. Determinação da idade gestacional com base em informações do estudo Nascer no Brasil. Cad. Saúde Pública. Vol 30. 59-70, 2014
- JYOTHSNA, B. et al. Gestational Age Correlation by Last Menstrual Period, Ultrasonography and Newballardscore. International Journal of Contemporary Medical Research. Vol 5. 7 ed; 77-83, 2018
FAQs
How can I calculate how many weeks pregnant I am?
- You take a pregnancy test and see the two stripes. The results are positive: you're pregnant. ...
- Gestational duration is counted from the first day of your last period. ...
- Your nearest Planned Parenthood health center is here to help you.
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.
How am I 4 weeks pregnant if I conceived 2 weeks ago? ›
Week 4 of pregnancy
For example, a fertilised egg may have implanted in your womb just 2 weeks ago, but if the first day of your last period was 4 weeks ago, this means you're officially four weeks pregnant! Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period.
How many weeks pregnant will I be on a certain date? ›
Pinpoint the first day of your LMP and count forwards to today's date — that tells you how many weeks and days into your pregnancy you are. To work out your EDD, use the LMP date and count forwards by 280 days.
How do I calculate how many weeks my baby is? ›
If you are counting your baby's age in months, then all you need to do is multiply the months by 4.345 because there are approximately 4.345 weeks in one month. But if you are counting your baby's age in years, then you will multiply the years by 52.176 because there are approximately 52.176 weeks in one year.
How many weeks will I know I am pregnant? ›
It is best to take a pregnancy test as soon after a missed period as possible. A pregnancy test may return a positive result as early as 10 days after conception. However, it typically takes about 3 weeks before there's enough hCG in the urine to produce a positive pregnancy test.
Does gestational age add two weeks? ›
While gestational age is measured from the first day of your last menstrual period, fetal age is calculated from the date of conception. This is during ovulation, which means that fetal age is about two weeks behind gestational age. This is the actual age of the fetus.
Why do doctors add 2 weeks on to pregnancy? ›
This is because pregnancy is counted from the first day of the woman's last period, not the date of conception which generally occurs 2 weeks later, followed by 5 to 7 days before it settles in the uterus.
How many weeks is full gestational age? ›
Pregnancy lasts for about 280 days or 40 weeks. A preterm or premature baby is delivered before 37 weeks of your pregnancy.
Is 5 weeks pregnant actually 3 weeks? ›
In week 5 of pregnancy, your baby is actually 3 weeks old and has finally "moved into" your uterus. Read on to discover when it is worth taking a pregnancy test, why your little one now looks like a little UFO, and other things that still need to happen at the start of the first trimester.
You might not be—here's why. Most OBs count pregnancy starting from the first day of your last menstrual period (LMP). (It's more accurate for doctors to estimate a due date this way.) So if you think you conceived about two weeks ago, you're probably at least four weeks pregnant—maybe even five.
When did I conceive based on how many weeks I am? ›
Generally, the due date is calculated 40 weeks after your last period. Therefore, if you have your due date, you can subtract 40 weeks from this date to determine your last menstrual period. Once you know the first day of your last period, you can add 11 to 21 days to figure out your conception date.
How to calculate gestational age in weeks? ›
Most pregnancies last about 40 weeks from the first day of the last menstrual period. The gestational age is based on the date of the last period, not the date of conception.
How do I calculate exact weeks of pregnancy? ›
Add 280 days (40 weeks) to the first day of your last menstrual period (assuming a 28-day cycle). Your menstrual period and ovulation are counted as the first two weeks of pregnancy.
How do I calculate the exact date I was pregnant? ›
What is the date of conception? Conception usually occurs 11 to 21 days following the first day of the previous period in a woman who has regular menstruation. Most women do not know the precise day of conception because it is difficult to predict when ovulation will occur.
How is weeks of pregnancy counted? ›
An unborn baby spends around 38 weeks in the womb, but the average length of pregnancy (gestation) is counted as 40 weeks. This is because pregnancy is counted from the first day of the woman's last period, not the date of conception, which generally occurs 2 weeks later.
How do you calculate how many weeks a baby is? ›
While in an ordinary year which is not a leap year, the number of weeks is 52 plus one day ( 365 / 7 = 52 weeks + 1 days ), leap years contain 52 weeks plus two days ( 366 / 7 = 52 weeks + 2 days ).
What is the exact weeks of pregnancy? ›
Pregnancy lasts for about 280 days or 40 weeks. A preterm or premature baby is delivered before 37 weeks of your pregnancy. Extremely preterm infants are born 23 through 28 weeks. Moderately preterm infants are born between 29 and 33 weeks.
How many weeks pregnant are you when you get a positive test? ›
In many cases, you might get a positive result from an at-home test as early as 10 days after conception. For a more accurate result, wait until after you've missed your period to take a test. Remember, if you take a test too soon, it could be negative even if you're pregnant.
