Pregnancy week by week. Maternity due date calculator

Finding out you’re pregnant can be one of the most exciting times in your life! As you prepare for your new addition, having a week-by-week guide to your pregnancy can help you understand what’s happening with your body and baby each step of the way. Use this handy pregnancy calendar to follow your pregnancy week-by-week and estimate your due date.

How Pregnancy Weeks Are Calculated

Pregnancy comes with its own timeline and lingo. Here’s a quick guide to how doctors calculate the weeks of pregnancy:

Gestational Age: This refers to how far along you are in pregnancy starting from the first day of your last menstrual period. Gestational age is used to estimate your due date and monitor your baby’s growth throughout pregnancy.
Fetal Age: This refers to how far along your baby is from the date of conception. Fetal age typically runs about two weeks behind your gestational age.
Trimesters: Pregnancy is divided into three trimesters of about 13 weeks each. The first trimester spans weeks 1-13, second trimester is weeks 14-27, and third trimester is weeks 28-40.

So in summary – gestational age is based on your LMP, fetal age starts at conception, and the weeks are grouped into three trimesters. Keeping these terms straight will help you follow along during prenatal visits!

Estimating Your Due Date

Wondering when to expect your new arrival? Here’s how to calculate your due date:

Date of Last Menstrual Period: The first day of your last period is used to estimate gestational age. If you have a regular 28-day cycle, you’d ovulate around day 14 and conceive close to that date.
Add 40 Weeks: Add 40 weeks (280 days) to the first day of your LMP. This will give you an estimated due date.
Adjust for Irregular Cycles: If your cycles are irregular, your LMP due date may need to be adjusted. Let your doctor know, as they may want to confirm gestational age with an ultrasound.
Note the Full Term Window: Babies are considered full term between weeks 37-42. So your due date is just an estimate – deliveries in this window are still considered full term.

To get a sense of when your little one may arrive, plug your LMP into a pregnancy due date calculator. But remember, only about 5% of babies are actually born on their due date!

Pregnancy Calendar Week-by-Week

Now that you have your due date, let’s look at the amazing changes happening with your body and baby week-by-week through your pregnancy:

First Trimester (Weeks 1-13)

These early weeks are full of big developmental milestones for your baby as they grow from a fertilized egg into a 1 inch fetus! Here are the highlights:

Week 1 & Week 2

Days 1-7 after ovulation/conception, the fertilized egg travels down the fallopian tube towards the uterus for implantation
The egg then implants in the uterine lining around day 7-10
Once implanted, the egg is called an embryo and pregnancy hormones start to rise

Week 3

Baby is now a ball of multiplying cells and the neural tube is forming (this will become the brain and spinal cord)
The amniotic sac and fluid begin to surround and protect the embryo
Placenta development begins to nourish the baby
Primitive heart tubes form and baby’s heart starts beating around day 21-22!

Week 4

Baby is the size of a poppyseed (~0.05 inches)
Facial features take shape including the mouth and tongue
Buds for arms and legs appear
Heart is pumping blood and continues developing
Umbilical cord connects baby to placenta
Major organs like kidneys begin forming
Embryo starts producing own blood, separate from mom’s

Week 5

Baby is the size of an apple seed (~0.13 inches)
Brain and face continue developing, including the eyes and ears
Yolk sac appears outside embryo to make blood cells until placenta takes over
Limb buds become arms and legs
Umbilical cord delivers oxygen and nutrients for baby’s growth

Week 6

Baby is about 1/4 inch long, roughly the size of a sweet pea
Brain development causes head to grow larger
Nose, mouth, and ears become more defined
Hands and feet grow out from arms and legs
Heart is fully formed, pumping blood
Kidneys start producing urine
Baby’s muscles start to move though you won’t feel movement yet

Week 7

Baby doubles in size this week to 1/2 inch long (~size of a blueberry)
Brain rapidly expands as head gets bigger
Nostrils and eyelids take shape, fingerprints form
Arm/leg buds now have joints for elbows/knees
Baby starts moving, though you still can’t feel it
Tooth buds form behind baby’s gums

Week 8

Baby is about the size of a raspberry at 0.6 – 0.7 inches
Bones start developing and hardening
Heart is pumping steadily and visible via ultrasound
Intestines, liver, and lungs continuing to develop
Limbs can bend at the joints
Facial features become more defined

Week 9

Baby grows to around 0.9 inches long, roughly the size of a grape
Fingers and toes are visible with nails forming
Baby’s trunk straightens out as neck develops
Facial features look more human, with upper lip and nostrils visible
Early tooth buds develop behind gums
Bones continue ossifying from soft cartilage
Heart is fully developed and beating twice as fast as yours!

Week 10

Baby reaches 1 inch in length, about the size of a kumquat
Cartilage and bone continue to solidify
Tooth buds and hair follicles form
Palmar creases form on hands and fingerprints are visible
Nipples form and reproductive organs start developing
Intestines grow longer and move into abdomen
Baby can hiccup and swallow
Heart pumps about 25 quarts of blood per day

Week 11

Baby doubles in size this week, measuring 2 inches (~size of a fig)
Facial features are more distinct, with visible eyes, nostrils, and developing lips
Tooth enamel and hair continue growing
Muscles strengthen allowing for more movement
Kidneys produce urine and start releasing it into amniotic fluid
Hands can open and close into fists
Reflexes develop like sucking, yawning, stretching

Week 12

Baby is about 2.5 inches long and weighs almost half an ounce
Fingerprints and footprints are fully formed
Bones continue hardening and limbs can extend and bend
Baby starts reflex movements like sucking and clasping hands
Reproductive organs visibly determine gender on ultrasound
Nerve endings develop allowing sensation
Intestines move more into abdomen and out of umbilical cord

Week 13

Baby is 3 inches long and over 1 ounce in weight
Bones and cartilage are fully formed
Fingerprints and footprints are visible
Baby can curl fingers around objects and suck thumb
Kidneys are developed and start producing urine
Baby’s liver starts making bile and bone marrow makes blood cells
Nerve connections form between the brain and organs
Most genetic defects are complete so risk of miscarriage drops

Congratulations, you made it through the first trimester! Your baby has gone through huge developmental milestones and is starting to look like a tiny human. As you move into the second trimester, start thinking about telling loved ones your big news!

Second Trimester (Weeks 14-27)

The second trimester brings some welcome relief from early pregnancy symptoms. This is often called the “honeymoon” phase. You’ll also start feeling your baby move around more which is an amazing milestone! Here are the highlights:

Week 14

Baby now measures about 3.5 inches and 2 ounces
Eyebrows, eyelashes, fingernails and hair form and fill out
Facial features become more defined as fat develops in cheeks
Skin looks wrinkly as more fat accumulates under it
Muscles and bones strengthen; baby can kick and curl up
Kidneys start producing urine which fills the amniotic fluid
Fine hair (lanugo) covers body for warmth and protection

Week 15

Baby is about 4 inches long from head to rump and weighs nearly 3 ounces.
Your baby’s skin is still thin and translucent, but a protective layer of fat is starting to build up underneath.
The heart is pumping around 25 quarts of blood per day as it continues maturing. You may be able to hear the heartbeat at your next prenatal appointment.
As muscles strengthen, your baby’s movements are getting more coordinated. You may start feeling the first flutters of movement this week!
External genitalia are forming if your baby is a boy. The reproductive organs on both boys and girls can now be clearly seen on an ultrasound.
Bones are hardening, except for the skull which needs to remain soft and flexible for delivery.
Eyebrows and eyelashes are beginning to fill in. Hair follicles are also forming on the head.
Your baby is actively swallowing the amniotic fluid which helps digestive system development.
The kidneys are developed enough to start producing small amounts of urine.
Your baby is continuing to grow longer as the torso straightens out. Those little arms and legs are starting to look more proportional to the body.

Week 16

Baby is about 4.5 inches long and over 3 ounces
Bones become harder and body fat increases
Baby begins to hear as inner ear structures develop
Heart steadily pumps about 25 quarts of blood per day
Lungs start developing surfactant to prepare for breathing
Skeletal muscles grow stronger allowing more complex movements
Facial features become more defined

Week 17

Baby measures nearly 5 inches long and 5 ounces in weight
Fat continues accumulating making wrinkles disappear
Tooth buds are forming tooth caps
Midline brain structures that control temperature, breathing, and digestion develop
Baby may startle in reaction to loud noises
Blood volume increases to about 17 ounces
Umbilical cord thickens and strengthens

Week 18

Baby is around 5.5 inches and weighs almost 7 ounces
Lanugo hair covers entire body
Sweat glands form causing vernix caseosa to develop on skin
Nerve endings proliferate allowing sense of touch
Baby may suck thumbs, yawn, stretch, and make faces
Heart pumps about 25 quarts of blood per day

Week 19

Baby measures over 6 inches crown to rump and 8+ ounces
Hearing continues to develop – baby may react to familiar voices and sounds
Bones and muscles grow stronger as they build up fat and tissue
Tooth enamel finishes forming and tooth buds await eruption
Reproductive organs show if baby is a girl or boy
A scan can detect fetal movement, swallowing, and urination

Week 20

Baby is around 10 ounces and 6.5 inches long
Skin is covered in vernix caseosa which protects and moisturizes
Fetal movements strengthen – you’ll feel kicks and somersaults!
Baby sleeps and wakes regularly
Sensory development advances – baby reacts to sounds, smells and touch
Hair follicles visible on eyebrows and scalp
Bone marrow starts making blood cells for immune system

Week 21

Baby now measures over 7 inches and 12+ ounces
Rapid brain development leads to increase in size
Hair continues growing longer and thicker, including eyebrows and lashes
Wrinkled skin starts smoothing out as more fat develops
Tastebuds form allowing baby to taste the amniotic fluid
Primitive reflexes like swallowing and sucking continue developing

Week 22

Baby is around 8 inches long and weighs nearly 1 pound
All five senses are developed – baby hears and responds to familiar voices and sounds
Skin is pink, smooth, and covered in vernix caseosa
Heart pumps 30 quarts of blood per day through fully formed circulatory system
Tooth buds and hair follicles continue developing
Thyroid and pituitary glands mature

Week 23

Baby is over 8 inches long and weighs 1 to 1 1⁄4 pounds
Fat stores build more this week making skin less wrinkled
Tooth buds contain tooth crowns, hair fills in eyebrows
Brain develops more folds and grooves
Muscle tone improves – baby can flex/extend arms and legs
Alveoli develop in lungs preparing for air breathing after birth

Week 24

Baby is around 9 inches long and over 1 1⁄2 pounds
Pupils can constrict, dilate and detect light entering eyes
Lungs and digestive system continue major development
Body hair and vernix caseosa coat skin
Baby’s circadian rhythms start syncing with light/dark cycles
Ear canals open allowing hearing development

Week 25

Baby measures nearly 10 inches and weighs almost 2 pounds
More brown fat accumulates under skin for warmth and energy
Brain develops further folds and grooves
Blood vessels form in lungs bringing oxygenated blood
Circadian rhythms regulate sleep/wake cycles
Taste buds allow tasting sweet amniotic fluid

Week 26

Baby is about 10 inches long and over 2 pounds
Lungs are nearly mature – baby would have high chance of surviving if born early
Eyes can open/close and sense changes in light
Brain wiring continues at rapid pace
Immune system ramps up production of antibodies and white blood cells
Baby’s kicks and movements are strong and more regular

Week 27

Baby weighs almost 2 1⁄2 pounds and is around 10 inches long
Brain development allows opening/closing eyes and responding to stimuli
Blood circulation transitions to lungs in preparation for breathing air
Limbs and organs grow proportional to head size
Skin is pink and smooth, with wrinkles almost gone
Sleep cycles sync up with awake/sleep times

The second trimester flies by quickly! Your baby is developing into a fully-formed little human that can hear, see, taste and respond to the world. Next up is the third trimester as baby continues to grow and prepare for birth!

Third Trimester (Weeks 28-40)

The final trimester is all about your baby growing rapidly in size and weight in preparation for birth. You’ll feel lots of movement and your belly will really expand. Here’s what’s happening:

Week 28

Baby weighs over 2 1⁄2 pounds and is around 10 to 11 inches long
Brain develops rapidly with new neuron formation
Eyes open and close, detecting light changes
Lungs nearing maturity in preparation for air breathing
Muscles and limbs fill out as fat and bone growth continue

Week 29

Baby is almost 3 pounds and around 11 inches long
Brain sees major development and expansion this week
Pupils react to light; eyes open/shut for sleep cycles
Blood cell production switches bone marrow to liver and spleen
Testes descend for baby boys
Kicks and movement are strong and regular

Week 30

Baby is over 3 pounds now and around 11 inches long
Brain circuity continues at rapid pace, synapses multiplying
Head hair may lose some lanugo while eyebrows fill in more
Lungs are nearly mature – baby would have high survival rate if born now
Limbs and organs are fully developed and proportional

Week 31

Baby weighs 3 1⁄2 pounds and is almost 12 inches long
Brain is very wrinkly as neuron production booms
Limbs are plumping up with fat layers under skin
Eyes can open and close, detecting light changes
Immune system strengthens along with blood cell production
Baby prepares for birth with head down position

Week 32

Baby is around 12 to 13 inches and over 4 pounds
Bones harden but skull stays soft and pliable for delivery
Fat layers build, making skin less wrinkly
Lungs are mature – baby would likely survive with medical support
Brain circuits continue multiplying at rapid pace
Body adjusts to accommodate birth soon

Week 33

Baby weighs over 4 1⁄2 pounds and is 13-14 inches long
Pupils react to light; eyes open for longer periods
Brain circuits and reflexes are developed and ready
Immune system is strengthened for fighting infections
Bones continue hardening while skull remains soft
Baby may settle into head down birthing position

Week 34

Baby is around 14 inches long and over 5 pounds now
Brain circuits are developed enough for basic functions
Lungs are mature – baby would likely survive birth
Head hair fills in more while lanugo decreases
Immune system can fight off infections after birth
Fingernails may extend past the fingertips

Week 35

Baby measures about 14 inches and 5 1⁄2 pounds
Brain will develop more complex functions after birth
Respiratory system is fully mature for life outside womb
Head hair thickens as lanugo sheds
Limbs plump up, becoming proportional
Immune system can fight infections independently

Week 36

Baby is around 15 inches and almost 6 pounds
Brain development continues but head is still soft
Eyes react to light and can focus on objects
Lungs fully mature, ready to breathe air
Limbs are plump with fat stores and muscle tone
Lanugo sheds except on shoulders and back

Week 37 (Early Term Birth)

Baby measures about 15-16 inches and over 6 pounds
Organs like liver and kidneys can process waste alone
Lungs are developed enough to breathe air right after birth
Head hair is plentiful with mostly lanugo shed
Baby can focus on faces and objects, detecting light

Week 38

Baby is around 16 inches and 6 1⁄2 pounds
Brain circuits continue strengthening and multiplying
Pupils react to light; eyes staying open more
Scalp hair is abundant; body sheds most lanugo
Muscles gain strength and coordination for delivery

Week 39 (cont.)

Limbs are filled out and proportional to body
Fat stores help baby regulate temperature after birth
Baby drops lower in pelvis in preparation for birth

Week 40 (Full Term Birth)

Baby is around 17-18 inches and 7 1/2 pounds
Brain circuits are developed for seeing, hearing, digesting, breathing etc.
Eyes can focus on faces and detect light from dark
Scalp hair is thick and usually dark
Limbs are proportional, with wrinkled skin as fat stores develop
Baby is ready for delivery!

Week 41 (Late Term Birth)

Baby measures about 18-19 inches and weighs 7+ to 8 pounds
Brain continues multiplying neurons and forming circuitry
Pupils adjust to light changes; eyes staying open more
Limbs fill out with fat while skin may look wrinkled
Lungs mature fully for breathing air after birth

Week 42 (Postterm Birth)

Baby is typically 8 pounds or more and around 19-20 inches
Brain circuits continue strengthening connections
Pupils react to light; eyes open and close for sleep cycles
Body fat increases while amniotic fluid volume decreases
Lungs are developed completely for breathing after birth
Baby is ready to deliver soon!

Congratulations – you made it full term! Your baby now has all the essential development needed to thrive outside your womb. Get ready to meet your little one very soon!

Key Pregnancy Milestones Week-by-Week

As you go through your pregnancy calendar, here are some of the biggest milestones to look forward to each week:

4 weeks: First heartbeats detected
8 weeks: Baby starts moving
10 weeks: Fingernails and major organs formed
12 weeks: Fetal movements strengthen, sex organs visible
16 weeks: Heart fully formed and pumping steady
20 weeks: Anatomy scan detects gender
24 weeks: Hearing fully develops, air sacs form in lungs
28 weeks: Eyes can open and close, respond to light
32 weeks: Rapid weight gain, lungs mature
36 weeks: Head is usually down in pelvis, ready for delivery
37+ weeks: Considered early term birth, lungs mature
40 weeks: Full term pregnancy! Baby is ready to be born

Pinpointing these exciting milestones on your calendar helps you understand all the changes with your baby week-by-week. Share your experiences with other expecting moms and enjoy every moment!

Tracking Your Pregnancy with a Week-by-Week Calendar

Keeping a week-by-week pregnancy calendar can help you remember and celebrate each milestone. Here are some tips:

Note your estimated due date and mark off each passing week
Use an app or written calendar to easily track each week
Record baby’s size and developmental milestones week-to-week
Write down symptoms, cravings, appointments and memories from each week
Take weekly bump photos to document your growing belly
Share updates and photos with your partner each week
Look back on your calendar to see just how far you’ve come

Baby Growth Week-by-Week

Track your baby’s size and weight week-by-week:

Week	Baby’s Size	Baby’s Weight
4 weeks	0.05 in (poppy seed)	<0.04 oz
8 weeks	0.6 – 0.7 in (raspberry)	<0.25 oz
12 weeks	2.5 in	0.5 oz
16 weeks	4.5 in	3 oz
20 weeks	6.5 in	10 oz
24 weeks	9 in	1.5 lbs
28 weeks	10-11 in	2.5 lbs
32 weeks	12-13 in	4 lbs
36 weeks	15 in	6 lbs
40 weeks	18-19 in	7.5 lbs

Trimester Symptoms and Changes

Here are some common symptoms and changes during each pregnancy trimester:

Trimester	Symptoms	Changes
First Trimester	Nausea, fatigue, food aversions, increased urination	Accelerated cell growth, hCG levels rise, fetal organs form
Second Trimester	Backache, abdominal swelling, stretch marks, dizziness, constipation	Belly expands, fetal movement felt, ultrasound detects gender
Third Trimester	Heartburn, swelling, insomnia, contractions, leaking fluid	Rapid fetal growth, lanugo sheds, baby drops into pelvis

Tracking symptoms and changes each trimester helps you understand what to expect during your 40 week pregnancy calendar! Let me know if you would like me to add any other tables or content.

Charting your journey week-by-week makes your pregnancy feel more real and helps you bond with baby long before delivery day. Use this week-by-week guide to learn about your amazing journey ahead!