Pregnancy Week-by-Week Calendar and Due Date Estimator

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:

  1. 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.
  2. Add 40 Weeks: Add 40 weeks (280 days) to the first day of your LMP. This will give you an estimated due date.
  3. 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.
  4. 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!