Due Date Calculator

You have taken a pregnancy test, and it appears to be positive. Now you may be wondering when exactly your baby will arrive. This is where due date calculators come in.

How do you want to calculate your due date?
Last Period
Conception date

Please note that Flo Health does not collect, process, or store any of the data that you enter while using these Tools. All calculations are done exclusively in your browser. Flo Health does not have access to the results. All data will be permanently erased after leaving or closing the page.

You will meet your baby on
Gestational age is
weeks and day

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.


Week 1

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.


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Week 2

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.

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Week 3

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.

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Week 4

At 4 weeks pregnant, your baby is the size of a poppy seed.

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.

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Week 5

At 5 weeks pregnant, your baby is the size of a sesame seed.

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.

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Week 6

At 6 weeks pregnant, your baby is the size of a lentil.

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.

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Week 7

At 7 weeks pregnant, your baby is the size of a blueberry.

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.

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Week 8

At 8 weeks pregnant, your baby is the size of a bean.

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.

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Week 9

At 9 weeks pregnant, your baby is the size of a cherry.

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.

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Week 10

At 10 weeks pregnant, your baby is the size of a kumquat.

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.

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Week 11

At 11 weeks pregnant, your baby is the size of a fig.

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.

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Week 12

At 12 weeks pregnant, your baby is the size of a plum.

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).

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Week 13

At 13 weeks pregnant, your baby is the size of a pea pod.

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.

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Week 14

At 14 weeks pregnant, your baby is the size of a peach.

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.

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Week 15

At 15 weeks pregnant, your baby is the size of an apple.

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!

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Week 16

At 16 weeks pregnant, your baby is the size of an avocado.

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!

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Week 17

At 17 weeks pregnant, your baby is the size of a potato.

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.

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Week 18

At 18 weeks pregnant, your baby is the size of a bell pepper.

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.

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Week 19

At 19 weeks pregnant, your baby is the size of a mango.

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.

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Week 20

At 20 weeks pregnant, your baby is the size of a grapefruit.

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.

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Week 21

At 21 weeks pregnant, your baby is the size of a banana.

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.

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Week 22

At 22 weeks pregnant, your baby is the size of a carrot.

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.

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Week 23

At 23 weeks pregnant, your baby is the size of a squash.

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.

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Week 24

At 24 weeks pregnant, your baby is the size of an eggplant.

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.

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Week 25

At 25 weeks pregnant, your baby is the size of a full ear of corn.

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.

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Week 26

At 26 weeks pregnant, your baby is the size of a beetroot.

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.

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Week 27

At 27 weeks pregnant, your baby is the size of a cauliflower.

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.

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Week 28

At 28 weeks pregnant, your baby is the size of a coconut.

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.

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Week 29

At 29 weeks pregnant, your baby is the size of a pomelo.

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.

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Week 30

At 30 weeks pregnant, your baby is the size of a head of cabbage.

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.

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Week 31

At 31 weeks pregnant, your baby is the size of a head of a zucchini.

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.

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Week 32

At 32 weeks pregnant, your baby is the size of a head of lettuce.

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.

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Week 33

At 33 weeks pregnant, your baby is the size of a pineapple.

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.

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Week 34

At 34 weeks pregnant, your baby is the size of a butternut squash.

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.

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Week 35

At 35 weeks pregnant, your baby is the size of a honeydew melon.

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!

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Week 36

At 36 weeks pregnant, your baby is the size of a papaya.

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!

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Week 37

At 37 weeks pregnant, your baby is the size of a head of romaine lettuce.

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.

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Week 38

At 38 weeks pregnant, your baby is the size of Swiss chard.

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.

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Week 39

At 39 weeks pregnant, your baby is the size of a small watermelon.

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?

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Week 40

At 40 weeks pregnant, your baby is the size of a mini watermelon.

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.

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Week 41

At 41 weeks pregnant, your baby is the size of a pumpkin.

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.

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Week 42

At 42 weeks pregnant, your baby is the size of a watermelon.

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.

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Due date calculation: How many weeks pregnant am I?

The due date, or estimated date of delivery (EDD), is the approximate date when labor is expected to begin.

As this date is just an estimate, you’ll probably start labor sometime in the two weeks before and after your due date.

In fact, only 1 in 20 people delivers on their estimated due date, which means only 5 percent of babies worldwide are born on their exact calculated date.

Gestational age vs fetal age

There are two ways to measure the age of a baby during pregnancy. To track pregnancy and calculate a due date, gestational age is used.

Gestation is the time between the conception date and birth, or how long a person is pregnant in weeks. 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 a premature baby.

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. 

You can read more about gestational age here and learn why it’s used to track pregnancy. 

How does the Flo Due Date Calculator work?

You can choose between two methods when calculating your due date with the help of this calculator:

  1. Due date by the last menstrual period. When using this method, the due date is calculated by adding 280 days (or 9 months, the common length of a pregnancy) to the first day of your last menstrual period. Note that this assumption is for a regular 28-day cycle (cycles can vary from 20 to 45 days), and the menstrual period and ovulation are considered to be the first two weeks of pregnancy. As this method is affected by the regularity of your menstrual cycle, it’s not 100-percent accurate.
  2. Due date by conception date (or ovulation). With this calculation, 266 days of pregnancy are added to the date you conceived.

More About Due Date Calculations 

Method 1: Due date by last menstrual period

There are several ways, or rules, to calculate the due date of a pregnancy by the last menstrual period in addition to the standard one used in the Flo calculator. The following rules are modifications of the standard formula to get more precise results, simply because the more information you can add to the calculation, the more accurate the due date may be. 

Read on if you’re curious about how these advanced formulas work in detail and how you can use them to calculate a more precise due date.

1. Naegele's rule

This is the standard method of calculating a due date for a pregnancy. Flo also uses Naegele’s rule as the main rule to calculate the due date.

The standard formula is as follows:
LMP + 280 days

This rule considers a regular menstrual cycle to be 28 days (it may vary from 20 to 45 days), with ovulation occurring around the 14th day of the menstrual cycle. If your cycle lasts longer, the estimated due date will be later. If you have a shorter cycle, your due date will be earlier.

2. Mittendorf-Williams rule

The Mittendorf-Williams rule is considered more advanced than Naegele’s rule, because the more info you provide, the more accurate the results will be.

This rule is based on a 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.

  1. First, determine the first day of your last menstrual period.
  2. Next, count back 3 calendar months from that date.
  3. Lastly, add 15 days to that date if it’s your first pregnancy, or add 10 days if it’s not your first pregnancy.

Short formulas look like this:

  • For first pregnancies:

LMP – 3 months + 15 days

  • For subsequent pregnancies:

LMP – 3 months + 10 days

3. Parikh's rule

Parikh’s formula is used for irregular cycles, and the expected date of delivery is calculated by adding 9 months to the last menstrual period, subtracting 21 days, and then adding the duration of previous cycles.

In short, use this formula: 
LMP + 280 days – 21 days + the length of previous cycles
*The average cycle length

Even though this formula is considered a modification of Naegele’s rule, by using it, the risk of any potential errors related to calculating your expected due date is greatly reduced.

4. Wood's rule

Wood’s method takes into consideration the individual length of the menstrual cycle as well as the number of pregnancies a person has experienced. 

1. First you calculate your expected due date.

  • For first pregnancies:

LMP + 12 months – (2 months and 14 days) = EDD

  • For subsequent pregnancies:

LMP + 12 months – (2 months and 18 days) = EDD

2. Then you use the expected due date in the equations below.

  • For cycles longer than 28 days:

EDD + (actual length of cycle – 28 days) = EDD

  • For cycles shorter than 28 days:

EDD – (28 days – actual length of cycle) = EDD

Method 2: Due date by day of conception

You might think that it would be easier to calculate your due date from the date you conceived by simply adding 266 days, but it is a little more complicated than that. Even if you know the exact date you had sex, the exact date of conception is almost never known. Why is that?

Because it can be challenging to determine the exact date of ovulation and thus the date of conception. Sperm can live in the female body for up to 5 days, and the egg can live for 24 hours after it’s released from the ovary.

Therefore, conception can occur several days after you’ve had unprotected intercourse.


EDD - Estimated Due Date 
LMP - Last Menstrual Period (the first day of your last menses)