Know your body. Own your health.
1,589,079 women joined Flo last week
Gestational age is the age of pregnancy and is counted from the first day of your LMP. So technically it includes two weeks during which you weren't pregnant yet.
At 1 week pregnant, you’re actually not pregnant yet. As your pregnancy is calculated from the first day of your last menstruation, your baby does not yet exist, and your body is preparing for the ovulation during which you’ll get pregnant.
At 2 weeks pregnant, you’re technically not pregnant yet. Right now there is a lone egg and a whole bunch of anxious sperm eager to fertilize the egg. Your uterus and the entire body are preparing for a big day of ovulation - the stage when you'll get pregnant.
Week 3 of pregnancy is the week when the implantation happens. Your body releases chorionic gonadotropin (hCG), which causes an increased production of estrogen and progesterone, and prevents new eggs in the ovaries from ripening. Very soon you'll start experiencing the first symptoms of pregnancy: missed period, nausea, breast changes.
At 4 weeks pregnant, your future baby has finally found his home for the next eight months. The blastocyst has arrived from a fallopian tube to your uterus. You can get a positive pregnancy test result at this stage.
By week 5, you should have missed your period, which is one of the most obvious sign you're expecting. Under the influence of hormonal changes, you can feel the first signs of pregnancy: breast swelling, fatigue, headache, and back pain.
Starting from pregnancy week 6, you may experience morning sickness. This is the result of hormonal changes occurring in your body. Malaise, breast swelling, darkening of the nipple areola, and frequent urination can bother you, too. In case of bleeding, you should consult your doctor.
At 7 weeks pregnant, symptoms start kicking in and your uterus almost doubles in size. Be prepared for a possible increase in nausea, fatigue, heartburn, and other pregnancy symptoms. Morning sickness may give a lot of trouble. Try to find some ways to cope with it.
At 8 weeks pregnant, you need to plan your first visit to the gynecologist. The doctor will prescribe the necessary tests and examinations for the first trimester of pregnancy. You may feel the growing discomfort of morning sickness. Try to be patient; it usually lasts until the 14th week only.
At 9 weeks pregnant, your baby is already about 0.6–0.7 in (16–18 mm) and weighs about 0.11 oz (3 g). The tail has disappeared; human features are becoming more distinct. The joints of his/her hands and legs can flex; the nipples and hair follicles are developing. Taste buds are beginning to form on the tongue, as well as primary tooth buds in the gums.
Week 10 of pregnancy is the time when almost all vital organs and tissues of your baby have formed. Now, they are beginning to function and grow rapidly. He or she can swallow amniotic fluid and move their arms and legs. The skin is getting covered with small hair and the fingers have tiny nails. Testes in boys already start to produce testosterone.
At 11 weeks pregnant, your baby has already reached 2 in (5 cm) in size. Now, his/her head is half the length of the body, but in the coming weeks, the body will grow enough to make up for it. The fetus skin is so thin and translucent that through it you can see an extensive network of vessels. Placental vessels are expanding to provide the fetus with necessary nutrients and oxygen.
At 12 weeks pregnant, your baby weighs about 0.49 oz (14 g). His/her vocal cords are forming, and kidneys are starting to produce urine, filling the bladder. Although you cannot feel it yet, you can see the baby during a sonogram screening (ultrasound).
Welcome to the last week of the first trimester! Most early pregnancy symptoms will soon be left behind. At 13 weeks pregnant, your baby is constantly growing. Now, he/she is more than 2.8 in (7 cm) from the top of his/her head to the coccyx.
At 14 weeks pregnant, your baby is developing rapidly. In a while, you will be able to feel them moving and kicking. Your body starts actively gaining weight. This occurs due to an increase in blood and lymph volume.
At 15 weeks pregnant, your baby your baby is actively drawing in amniotic fluid through his/her nose. Very soon you'll start looking pregnant indeed as your uterus has risen from your pelvic region to your lower abdomen. Time to plan pregnancy shopping!
You’re on week 16 of your pregnancy, and things are really starting to gear up! Your tiny baby is not so tiny anymore, and it most definitely looks like a human baby now. By week 16 of your pregnancy, you’re 4 months in. That means you’re nearly halfway there and only have 5 more months to go!
If you’ve been enjoying a relatively subtle pregnancy with very little belly to show for it, that’s probably over now! Your waist will gradually disappear as your uterus moves upwards and out of your pelvis.
If you’ve been astonished by your baby’s rapid growth and weight gain over the last few weeks, by week 18 this will start to level off a little — but there’s still lots of big news in your little one’s early life! At this stage, he or she can yawn, stretch, and even make facial expressions like frowning. The baby’s sense of taste is developing, and taste buds can now distinguish between sweet and bitter.
At 19 weeks pregnant, your rounded belly is very noticeable. The first hair appears on the baby's head, and the brain areas responsible for the senses — tactile, gustatory, olfactory, visual and auditory — are developing rapidly.
Congratulations! You are halfway to meeting your baby. The baby's legs have almost straightened, so from now on, he/she will be measured from head to toe.
As a 21 week pregnant woman, you have crossed the halfway line on your journey to becoming a mother. Your baby is getting bigger. You can now definitely feel her presence as she explores the real estate that you’ve prepared for her.
If you are entering the 22nd week of your pregnancy, without doubts it is getting crowded in there! Your baby is growing and invading your space. And your uterus stretches to about 2 cm (0.8 in) above your belly button to fit your growing baby.
For many women, being 23 weeks pregnant is an exciting time because you may finally be showing your baby bump! Among other things, your baby’s eyes and lips are taking shape. They will begin to gain weight more weight which will eventually fill out their wrinkly skin.
At 24 weeks pregnant, your baby is almost a foot long. You could be experiencing a tingling sensation in your joints, which is known as carpal tunnel syndrome. It is a common condition during pregnancy which occurs due to fluid build-up in your joints which results in compression of the median nerve.
Once you reach week 25 of your pregnancy, you’ll be nearing the end of your second trimester. It can feel like times flies! At 25 weeks pregnant, you’re approximately 5 months and 2 weeks along. Your baby has been growing steadily and even though it’s still not ready, it won’t be long before it comes into the world.
You’re likely to put on between 16 and 22 pounds by now. At one point during this week, your baby will open his or her eyes for the first time. He or she is not yet able to see anything inside of the uterus but will blink closing and opening his or her eyes when falling asleep and waking up.
The 27th week of the pregnancy marks the final two weeks of the second trimester. If your baby is more active at night you might suffer from insomnia and have trouble sleeping. Compensate for the lack of sleep time during the night by napping during the day more when the baby is sleeping.
At 28 weeks you are now entering the third trimester of your pregnancy. At this stage, your baby is pretty well-developed. Her organs, tissues, and nerves continue to grow, but she already has all of the systems necessary for survival outside the uterus. Towards the end of the pregnancy, babies start to recognize familiar sounds and voices.
At 29 weeks pregnant, you're likely to develop varicose veins like 40 percent of expectant moms. It's also a good time to start doing a kick count. Let your doctor or midwife know if you notice that your baby is becoming less active.
At 30 weeks pregnant, you are likely to experience shortness of breath. Your baby is still up high near your rib and is waiting a bit – it is soon expected to drop down into your pelvis.
At 31 weeks pregnant, your breasts can get leaky producing the first baby’s food – colostrum. This is one of the symptoms that your body is getting ready for the big day. You are likely to experience shortness of breath. This week your baby is going through major nerve and brain development.
At 32 weeks pregnant, your body may start flexing its muscles preparing for the big day. Your baby is also preparing for her debut mastering the skills she’ll need to thrive outside your womb: swallowing, breathing, sucking.
At 33 weeks pregnant, you may notice that your baby’s movements are affected by your daily routine. Your belly continues to grow and it’s getting even more troublesome to find a comfortable sitting or sleeping position.
At 34 weeks pregnant, your breasts could start leaking small amounts of yellowish colostrum. Your baby is already the size of a school bag and weighs as a melon. If you’re worried about your safety at work, time to talk to your employer about maternity benefits.
At 35 weeks pregnant, you may know how your baby’s moving in your womb just by looking at your bump. It can you give you some discomfort and make you a bit breathless. At this point, many moms can’t wait for the baby to get here, while others are feeling a bit anxious about giving birth. Both feelings are completely normal!
At 36 weeks pregnant, your baby is sleeping between 60 and 80% of the time. It has finally moved into your pelvic cavity, the pressure on your diaphragm is released, and lightening happens. Your baby can now open its eyes, suck its thumb, breathe, and recognize voices!
Welcome to your 37th week of pregnancy, and congratulations! The baby moves further into the pelvis. It is considered to be ‘at-term’ and can actually arrive any day now. Make sure you are ready for the arrival of a new family member.
At 38 weeks pregnant, you can find yourself spending the whole life peeing. The pressure on your bladder is tremendous. Your baby is a fully functioning little human and your placenta is fully grown.
Welcome to the week 39 of pregnancy! Your baby is full term, meaning that it is fully developed and is only waiting for the right time to make an entrance into the world. Have you prepared everything that is needed to welcome your baby?
At 40 weeks pregnant, you may feel disappointed that your due date has come and gone. Don’t panic and make the last preparations for a new human who’ll soon join the world.
At week 41 of pregnancy, you might be dying out of the desire to give birth and see your baby. But rest assured that plenty of moms-to-be go past their due date and everything turns out just fine.
When a pregnancy lasts for 42 weeks or more it is referred to as a post-term pregnancy. While not many studies exist that prove why some women’s pregnancy lasts for 42 weeks, medical experts believe that factors such as hormones, genetics, and even obesity can be the cause.
If you’ve taken a pregnancy test and it appears to be positive, you might be wondering what happens next. That’s where our due date calculator or due date predictor comes in.
By using some basic information about your last period and cycle length, our pregnancy calculator can help you work out your estimated due date (EDD — aka when you might meet your baby). This information is also useful if you’re thinking about the baby’s due date timings before you start trying to conceive.
Try using our EDD calculator now and then scroll down for more on how due dates (and pregnancy) are calculated, plus information on when you could have conceived and how far along you might be.
One of the first questions you’ll probably have after discovering that you’re pregnant is “How pregnant am I?” Interestingly, there are two ways to measure the age of a baby during pregnancy — gestational age vs fetal age — but health care providers generally use gestational age only because it’s deemed more accurate.
More on those below, but when you know how far into your pregnancy you are, you can get a clearer idea of your expected date of delivery. This is another name for a due date, meaning your EDD is the approximate date when labor is expected to begin. As we’ll explain if you scroll down, this date is really just an estimate, so you can expect to go into labor anytime in the two weeks before and after your due date.
To track pregnancy and calculate a due date, doctors use gestational age. Gestation is how long a person is pregnant in weeks, and gestational age is measured from the last menstrual period (LMP) — the first day of your last period — to the current date in weeks.
In general, pregnancies last anywhere from 38 to 42 weeks (or around 280 days). If a baby is born before 37 weeks, they are considered premature.
The other method of measurement is fetal age. While gestational age measures how far along a pregnancy is in weeks, fetal age is the actual age of the growing baby. To calculate this, you work out the amount of time from the date of conception (which is around two weeks later than your LMP in a 28-day cycle but varies depending on cycle length) to the current date in weeks. However, this is a far less common measurement for pregnancy because it’s often hard to pinpoint exactly when you ovulated (and therefore the moment of conception).
Lots of us assume that a pregnancy is exactly nine months long, but that’s not the case. To work out how to calculate pregnancy weeks, there’s a little more to it.
“The nine months of a pregnancy are actually 40 weeks,” Dr. Charlsie Celestine, Flo board member, obstetrician, and gynecologist (OB-GYN), explains. “The due date is 40 weeks from the first day of your last menstrual period. But some women can go beyond that to 41 weeks.”
In fact, the first thing you’ll likely notice when you let your health care provider know you are pregnant is that pregnancy is calculated in weeks rather than months. And your baby’s estimated due date falls on the 40th week, when you’ll actually be around 10 months pregnant.
That’s to account for the fact that pregnancy is measured according to gestational age, not fetal age. So that means you count pregnancy from your LMP, not the date you conceived, adding an extra two weeks even though you weren’t technically pregnant then. Also, this method recognizes that not all months have the same number of days, so you’ll likely still be pregnant at nine months.
You might also see figures like 13/5 or 13+5 in your doctor notes. Pregnancy is counted in complete weeks, so 13/5, 13+5, or a variation of this would mean you’re 13 weeks and 5 days pregnant. Learn more about how you count pregnancy weeks here.
Your health care provider will usually calculate your due date based on one or a combination of the following methods, so let’s find out more about how they work.
As we now know, the most commonly used method to calculate due date is to count “40 weeks from the first day of your LMP,” Dr. Celestine says, adding that this is usually done at your first appointment.
This method is also known as Naegele’s rule. “You calculate [EDD] using the first day of the last menstrual period [adding exactly one year to it], add seven days to that, and then subtract three months,” she explains.
It’s worth noting that this rule considers a regular menstrual cycle to be 28 days long, but it’s totally normal for a person’s cycle to vary from anywhere between 21 and 45 days. If your cycle lasts longer, the estimated due date will likely be later. If you have a shorter cycle, your due date may be earlier.
“More commonly, I use a pregnancy wheel using the first day of the menses [period],” says Dr. Celestine, explaining how she tends to work out the due date in her patients.
A pregnancy wheel or gestation calculator is a simple calendar that works out your EDD or baby’s birth date based on different inputs, such as your LMP. OB-GYNs can also use a pregnancy wheel as a pregnancy timeline calculator to work out when you’ll have certain scans and screenings, along with your trimester dates.
As you’ve seen above, there are numerous ways to calculate an estimated due date — most involving the date your last period started. But an ultrasound scan in the first trimester is used to check that the dating based on the last menstrual period is correct. This is especially important if your period doesn’t always arrive at the same time each month.
“The LMP is compared to an ultrasound because some women have irregular cycles [and some can’t remember when their last period happened], so their LMP is not the most accurate,” Dr. Celestine explains.
“On ultrasound, I would measure the length of the fetus, called the ‘crown–rump length,’ in the first trimester to get the gestational age or due date. I then compare that date to the result I would get from just using the LMP.
“If the two dates are within five days of each other, and the pregnancy is less than nine weeks along, then we use the due date calculated by the period, not the ultrasound. But for a greater-than-five-day difference, we use the ultrasound.”
Already had your first ultrasound scan? Then you can use our Due Date by Ultrasound Calculator.
Find out what you can do with our Health Assistant
While most OB-GYNs use a combination of Naegele’s rule and the pregnancy wheel to determine EDD — and then use an ultrasound to confirm it — there are some other theories and methods about how to calculate due date. However, it’s worth noting that none of the following are currently used by health care providers to work out the due date, as there’s a lack of scientific evidence behind them. The theories are as follows:
One theory on how to calculate due date, also using LMP, is the Mittendorf-Williams rule. This is based on an old study from 1990, and there haven’t been any more recent studies to suggest it’s accurate, which is why health care professionals don’t commonly use it to predict EDD.
This rule is based on a decades-old study that showed that first pregnancies tend to be slightly longer (an average of 288 days from LMP), and for subsequent pregnancies, the delivery date is an average of 283 days from LMP. So …
Parikh’s rule is another theory that lacks scientific evidence to back it up, so medical practitioners don’t commonly use it to calculate due date either. The idea goes, however, that it can help predict due date in those who have irregular cycles. So, how does it work?
Loosely designed around Naegele’s rule, the expected date of delivery in Parikh’s rule is calculated by adding nine months to the date of your last menstrual period, subtracting 21 days, and then adding the duration of previous cycles. In short, use this formula:
Wood’s method considers the individual length of the menstrual cycle, as well as the number of pregnancies a person has experienced. However, there is also minimal research on this and its effectiveness. To work it out …
If your cycle runs like clockwork, and you were having sex to get pregnant at a specific time, then you might have an inkling that conception happened on a certain date. But Dr. Celestine says that the conception date “isn’t used medically to calculate due date” because it’s often not accurate.
That makes sense because we know sperm can live in the female body for up to five days, an egg can still be fertilized for up to 24 hours after its release from the ovary, and ovulation doesn’t always happen on the same day each month (you can find out when you’re likely to be ovulating each month using our online ovulation calculator). That means you can still get pregnant several days after you’ve had unprotected sex.
If you’ve had IVF, then your baby’s due date is calculated slightly differently, depending on:
The good news is that IVF due dates are generally more accurate because you’ll know exactly when you had your embryo transfer or medically conceived, although no due date is 100% accurate. Use our IVF Due Date Calculator to work out when you could be due.
There’s a lot that centers around it, so you’re probably wondering how likely it is that you’ll give birth on your due date. “The accuracy of the due date depends on how early in the pregnancy it was calculated and how predictable your menstrual cycle is,” Dr. Celestine explains.
“The earlier you see an OB-GYN to establish care for the pregnancy, the better, because the due date [from an ultrasound scan] is more accurate early in pregnancy compared to later. It’s rare for a baby to be born exactly on their due date [only around 4% of babies are]. Usually, delivery happens within a week before or after. But there are many babies also born prematurely, [along with] medical reasons why you might need to be induced for labor early, so it really depends on the individual.”
As Dr. Celestine explains, it’s hard to predict the exact day you got pregnant (unless you’ve successfully conceived after fertility treatment).
“It’s all an estimate because it depends on the day you ovulated,” she says. “If you know your cycle length and it’s always the same, then usually midway through your cycle prior to pregnancy is when conception occurred.”
Lots of people will calculate their due date as one of the first things they do after finding out they’re pregnant. And that’s useful for having a rough idea of when your baby will arrive, but it’s worth noting that this should be confirmed by your health care provider. They will use information about your last menstrual period, plus your first ultrasound, to work out your EDD, and once this has been calculated, it’s rare for your due date to change.
It’s so unusual for the due date to change after your first ultrasound scan because knowing the gestational age holds a lot of importance in monitoring the health of a pregnancy. “There are certain tests that need to be performed at certain gestational ages during a pregnancy,” Dr. Celestine explains. “Knowing how far along you are is also important for following the growth of the baby, when we can expect to deliver, and much, much more.”
Some people like to be organized, and there’s nothing wrong with that. But it can be quite tricky to plan a due date because there are so many factors at play with conception that you (and your partner) don’t have control over.
Nobody ever knows for certain when they will conceive. Even if you pinpoint your fertile window and have plenty of unprotected sex during that time, you still won’t know for certain whether or not that will be the month you get pregnant. That’s because so much of it is up to chance. For context, 45% of young couples (under 35) will conceive after three cycles, and 65% will get pregnant after six cycles. So while you might want to plan to have a baby in a certain month, all you can really do is try.
And even if you do manage to conceive at a time that gives you your ideal due date, remember that your EDD is just an estimate. Babies come on their own schedule. While the “average” pregnancy lasts 40 weeks from the day of the last menstrual period, it is normal for babies to come anywhere from 37 to 42 weeks, so it’s best not to focus too much on a specific due date.
Whether you’re currently pregnant or trying to work out when you’d be due if you got pregnant today, Flo can help. Use our Trying to Conceive mode to optimize your chances of getting pregnant by tracking your periods, which can help to identify your most fertile days. Alternatively, switch to Pregnancy Mode to get week-by-week updates for both your body and your baby.
Try some of Flo's other online tools, including our hCG calculator, our pregnancy test calculator, and our period calculator.
“Extremely Preterm Birth.” The American College of Obstetricians and Gynecologists, www.acog.org/womens-health/faqs/extremely-preterm-birth. Accessed 30 Aug. 2022.
“Heavy and Abnormal Periods.” The American College of Obstetricians and Gynecologists, www.acog.org/womens-health/faqs/heavy-and-abnormal-periods. Accessed 30 Aug. 2022.
“How Long Does Pregnancy Last?” The American College of Obstetricians and Gynecologists, www.acog.org/womens-health/experts-and-stories/ask-acog/how-long-does-pregnancy-last. Accessed 13 July 2022.
Jukic, A. M., et al. “Length of Human Pregnancy and Contributors to Its Natural Variation.” Human Reproduction, vol. 28, no. 10, Oct. 2013, pp. 2848–55.
Khedri, Parichehr, et al. “Comparison of the First Trimester Ultrasound and Parikh’s Formula in Determining the Expected Date of Delivery: A Prospective Study.” BMC Pregnancy and Childbirth, vol. 21, 30. Apr. 2021, jbrms.medilam.ac.ir/article-1-152-en.pdf.
Mittendorf, R., et al. “Predictors of Human Gestational Length.” American Journal of Obstetrics and Gynecology, vol. 168, no. 2, Feb. 1993, pp. 480–84.
Morgan, John A., and Danielle B. Cooper. “Pregnancy Dating.” StatPearls, StatPearls Publishing, 2021.
“Screening Tests in Pregnancy.” NHS, www.nhs.uk/pregnancy/your-pregnancy-care/screening-tests/. Accessed 13 July 2022.