How many weeks is each trimester of pregnancy?

The first trimester runs from week 1 to week 13, the second trimester from week 14 to week 27, and the third trimester from week 28 to birth (usually around week 40). Each trimester lasts roughly three months. Because pregnancy is counted from the first day of your last period, you're considered about 4 weeks pregnant around the time of your missed period.

How big is my baby right now?

Baby size is often described using fruits and vegetables. In the first trimester your baby grows from a poppy seed (around week 4) to a peapod (around week 13). By 20 weeks they're about the size of a banana, and by full term they're roughly the size of a small watermelon, about 18-20 inches long and 6-9 pounds. A pregnancy tracker app can show you a personalized size comparison for your exact week.

When can I feel my baby move?

Most people first feel their baby move, a sensation called quickening, between 16 and 22 weeks of pregnancy. First-time parents often notice it later than those who've been pregnant before, because they're less sure what to expect. Early movements feel like flutters, bubbles, or gentle taps. If you've felt regular movement and then notice a clear decrease, contact your provider right away.

How many weeks is 9 months pregnant?

Nine months of pregnancy is roughly 36 to 40 weeks, since each month is a little over four weeks long. This is why a 40-week pregnancy is often described as nine months even though the math doesn't divide evenly. Full term is considered 39 to 40 weeks, and babies born from 37 weeks are called early term.

Is my due date exact?

No, a due date is an estimate based on a 40-week pregnancy counted from your last period, and it marks the center of a window rather than a fixed deadline. Only about 1 in 20 babies arrives on their exact due date. Most healthy babies are born anytime between 37 and 42 weeks. Your provider may adjust your due date slightly after an early ultrasound.

Pregnancy Week by Week: Symptoms & Baby Size

Q: What pregnancy symptoms are normal versus a reason to call my doctor?

Nausea, fatigue, breast tenderness, mild cramping, backache, and occasional Braxton Hicks contractions are common and usually normal. You should contact your doctor or midwife right away for vaginal bleeding, severe or persistent abdominal pain, severe vomiting that prevents you from keeping fluids down, a noticeable drop in your baby's movement in later pregnancy, a severe headache with vision changes or swelling, or anything that feels wrong. Every pregnancy is different, so when in doubt, always call.

From the moment two lines appear on a test, one question tends to repeat on a loop: what's happening inside me right now? Pregnancy is measured in weeks, not months, and each week brings tiny, often invisible changes, your baby growing from a poppy seed to a watermelon, and your body adjusting in ways that can feel exciting one day and overwhelming the next. This guide walks you through pregnancy week by week so you always know roughly where you are, what your baby is up to, and what's normal to feel.

We've grouped the journey by trimester, with the key milestones, baby size by week, and the most common weeks pregnant symptoms at each stage. Pregnancy is counted from the first day of your last menstrual period (LMP), which is why you're considered "4 weeks pregnant" around the time of your missed period, even though conception happened about two weeks earlier. A full-term pregnancy runs about 40 weeks. Remember as you read: every pregnancy is different, and these are general patterns, not a checklist you must match.

This guide is general information, not medical advice

The descriptions here are typical patterns, not rules. Your symptoms, timing, and baby's size can all vary and still be perfectly healthy. Always contact your doctor or midwife if something feels wrong, and use the urgent-symptom checklist near the end of this guide. When in doubt, call, that's exactly what your care team is there for.

How pregnancy weeks, months, and trimesters fit together

Pregnancy is divided into three trimesters, each roughly three months long. Because months and weeks don't line up neatly, "how many weeks is X months" is one of the most-searched pregnancy questions, so here's the quick map:

First trimester: weeks 1 to 13 (roughly months 1, 2, and 3). The foundation stage, when all of your baby's major organs begin to form.
Second trimester: weeks 14 to 27 (roughly months 4, 5, and 6). Often the most comfortable stretch, sometimes called the "honeymoon" phase.
Third trimester: weeks 28 to 40+ (roughly months 7, 8, and 9). The home stretch, when your baby gains weight and gets ready to meet you.

A handy rule of thumb: each month of pregnancy is a little over four weeks, so 12 weeks is about three months, 20 weeks is about halfway, and 36 weeks is roughly nine months. Your due date is an estimate, only about 1 in 20 babies actually arrives on it, so think of it as the center of a window rather than a deadline.

First trimester (weeks 1-13): big changes, tiny baby

This is the busiest developmental period of the entire pregnancy, even though there's little to show on the outside yet. By the end of the first trimester your baby has gone from a cluster of cells to a recognizable little human with a beating heart, fingers, and toes.

Baby size by week, first trimester

Weeks 4-5: about the size of a poppy seed to a sesame seed. The neural tube (future brain and spine) is forming.
Weeks 6-7: a lentil to a blueberry. A heartbeat may be visible on an early ultrasound.
Weeks 8-9: a raspberry to a grape. Tiny arm and leg buds lengthen into limbs.
Weeks 10-11: a strawberry to a lime. Vital organs are in place and starting to function.
Weeks 12-13: a plum to a peapod, around 3 inches long. Your baby can make tiny movements, though you won't feel them yet.

Common first-trimester symptoms

The pregnancy hormones hCG and progesterone surge in these weeks, and they're behind most of what you feel. Common, normal symptoms include:

Nausea and "morning" sickness (which can strike any time of day), often peaking around weeks 8-10.
Deep fatigue, the kind that makes a 7 p.m. bedtime sound wonderful.
Tender, swollen breasts and darkening around the nipples.
Frequent urination, food aversions or cravings, heightened sense of smell, and mood swings.
Light spotting around the time of your missed period (implantation), which is often normal, though any bleeding is worth mentioning to your provider.

If you have severe, relentless vomiting that stops you keeping fluids down, you may have hyperemesis gravidarum, which needs medical care, so contact your provider rather than toughing it out. Want a deeper, week-range-by-week-range look at this stage? Our companion first trimester symptoms guide goes through it in detail.

Start your prenatal care now

If you haven't already, book your first prenatal appointment and take a daily prenatal vitamin with folic acid, which helps protect your baby's developing brain and spine. Starting early, ideally even before conception, makes a real difference.

Second trimester (weeks 14-27): the comfortable middle

For many people, the second trimester is when pregnancy starts to feel genuinely joyful. Nausea usually eases, energy returns, and you'll likely start showing. This is also when you'll have your detailed anatomy scan and, if you choose, can learn your baby's sex.

Baby size by week, second trimester

Weeks 14-16: a lemon to an avocado. Your baby can make facial expressions and may start sucking a thumb.
Weeks 17-19: a pomegranate to a mango. A protective coating (vernix) and fine hair (lanugo) develop.
Weeks 20-22: a banana to a small papaya, around the halfway mark and roughly 10 inches long.
Weeks 23-25: a large mango to an ear of corn. Your baby is gaining fat and practicing breathing motions.
Weeks 26-27: a head of lettuce to a cauliflower. Eyes begin to open and lungs continue maturing.

Common second-trimester symptoms

As your bump grows, the symptom mix shifts. You might notice:

Quickening, those first fluttery baby movements, often felt between weeks 16 and 22 (sometimes later for first-time parents).
A visible bump, plus round ligament pain (sharp twinges in the lower belly as muscles stretch).
Backaches, mild swelling, and stuffy nose from increased blood volume.
Skin changes like a darker line down the belly (linea nigra) and a pregnancy "glow."
Braxton Hicks contractions, occasional painless tightening as your uterus practices.

Around weeks 18-22 you'll typically have your anatomy ultrasound, a detailed check of your baby's organs, growth, and the placenta. It's a reassuring milestone for most parents.

Track your pregnancy week by week with Babymind

The Babymind Pregnancy Tracker gives you a personalized week-by-week timeline, fruit-and-veggie baby size comparisons, and built-in tools like a kick counter and contraction timer, so you always know what's happening and what to watch for.

Get the Babymind Pregnancy Tracker

Third trimester (weeks 28-40+): the home stretch

In the final trimester your baby does most of their growing in weight and prepares for life outside the womb. You'll see your provider more often now, and you'll start counting down to the big day.

Baby size by week, third trimester

Weeks 28-30: an eggplant to a large cabbage. The brain develops rapidly and your baby can open their eyes.
Weeks 31-33: a coconut to a pineapple. Bones harden, though the skull stays soft for birth.
Weeks 34-36: a cantaloupe to a honeydew melon. Your baby often settles head-down in preparation for delivery.
Weeks 37-40: from a winter melon to a small watermelon, around 18-20 inches and 6-9 pounds at term. At 37 weeks your baby is considered "early term," and full term is 39-40 weeks.

Common third-trimester symptoms

This stage asks the most of your body. Typical experiences include:

Shortness of breath and heartburn as your growing uterus crowds your lungs and stomach.
Swelling in the feet and ankles, trouble sleeping, and frequent bathroom trips as the baby presses on your bladder.
Stronger Braxton Hicks and, later, real contractions.
Pelvic pressure and "lightening" when the baby drops lower, sometimes easing your breathing.
Nesting energy, a sudden urge to clean and organize before baby arrives.

From around 28 weeks, your provider may ask you to pay attention to your baby's movement patterns. A noticeable drop in movement is one of the most important things to report right away, so trust your instincts and call if your baby seems quieter than usual.

What to do at every stage

Wherever you are in your pregnancy, a few habits support you and your baby throughout:

Keep all prenatal appointments and take your recommended prenatal vitamins.
Eat a varied, balanced diet, stay hydrated, and follow food-safety guidance for pregnancy.
Move gently and regularly if your provider approves, walking, swimming, and prenatal yoga are popular choices.
Avoid alcohol, smoking, and recreational drugs, and check with your provider before taking any medication.
Rest when you can and ask for help, growing a human is real work.

Call your doctor or midwife right away if you have

Vaginal bleeding, severe or persistent abdominal pain, severe vomiting that prevents you from keeping fluids down, a sudden decrease in or absence of fetal movement (in later pregnancy), a bad headache with vision changes or swelling, signs of preterm labor, your water breaking, a fever, or anything that simply feels wrong. It's always okay to call, even at 3 a.m. Trust your gut, you know your body best.

Pregnancy is a remarkable, sometimes bewildering stretch of life, and following it week by week can turn the unknown into something you can picture and prepare for. Some weeks will feel magical and some will feel endless, and both are completely normal. Lean on your care team, take it one week at a time, and remember that millions of parents have walked this exact path before you, you've got this.

Pregnancy week by week: what happens each week