Pregnancy Week by Week
Reviewed by Safi Allah Khan
Medically reviewed by: Safi Allah Khan · Written by the Momi team · Last updated 20 October 2026
Quick answer: Pregnancy week by week runs from week 1, counted from the first day of your last period, to your due date at 40 weeks. The first trimester ends at 13 weeks 6 days, the second at 27 weeks 6 days, and the third lasts until birth. Each week below shows your baby's typical size, development and common symptoms.
Use this page as your map. Find your week in the chart, open the week page for details, and use the free tools if you aren't sure which week you're in.
How pregnancy weeks are counted
Doctors and midwives count pregnancy from the first day of your last menstrual period (LMP). That makes the start date easy to pin down, but it means the first two weeks happen before you conceive. Your due date is 280 days, or 40 weeks, after your LMP.
Weeks are written as completed weeks plus days. "12+3" means 12 full weeks and 3 days, so you are in your 13th week. This trips up a lot of people: at 12+3 you are "12 weeks pregnant", even though it's the 13th week.
Don't know your week? Use How Many Weeks Pregnant Am I? or the due date calculator. If an early ultrasound gives you a different due date, ACOG recommends using the scan date, since a first-trimester scan is the most accurate way to date a pregnancy.
Pregnancy week by week chart
Sizes are typical averages from standard fetal growth references. Healthy babies vary, and your scan measurements may be different. Before about 20 weeks, length is measured from the top of the head to the bottom (crown to rump). After that, it's measured head to heel, which is why the numbers jump at week 20.
| Week | Trimester | Baby is about the size of | Length | Weight | Milestone |
|---|---|---|---|---|---|
| 1 | 1st | No baby yet | – | – | Pregnancy dating starts with your period |
| 2 | 1st | No baby yet | – | – | Ovulation and possible conception |
| 3 | 1st | No baby yet | – | – | Fertilisation and implantation |
| 4 | 1st | a poppy seed | about 1 mm (0.04 in) | – | Positive test possible |
| 5 | 1st | a sesame seed | about 2 mm (0.08 in) | – | Neural tube and heart begin forming |
| 6 | 1st | a lentil | about 4–6 mm (0.2 in) | – | Heart activity may show on scan |
| 7 | 1st | a blueberry | about 1 cm (0.4 in) | – | Arm and leg buds |
| 8 | 1st | a raspberry | about 1.6 cm (0.6 in) | – | End of embryo's first stage |
| 9 | 1st | a grape | about 2.3 cm (0.9 in) | – | Fingers and toes separating |
| 10 | 1st | a kumquat | about 3.1 cm (1.2 in) | about 4 g (0.1 oz) | All major organs forming |
| 11 | 1st | a fig | about 4.1 cm (1.6 in) | about 7 g (0.25 oz) | Now called a fetus |
| 12 | 1st | a lime | about 5.4 cm (2.1 in) | about 14 g (0.5 oz) | Dating scan window |
| 13 | 1st | a lemon | about 7.4 cm (2.9 in) | about 23 g (0.8 oz) | Last week of trimester one |
| 14 | 2nd | a nectarine | about 8.7 cm (3.4 in) | about 43 g (1.5 oz) | Second trimester begins |
| 15 | 2nd | an apple | about 10 cm (4 in) | about 70 g (2.5 oz) | Bones hardening |
| 16 | 2nd | an avocado | about 11.6 cm (4.6 in) | about 100 g (3.5 oz) | First movements possible |
| 17 | 2nd | a pear | about 13 cm (5.1 in) | about 140 g (5 oz) | Fat stores start |
| 18 | 2nd | a bell pepper | about 14.2 cm (5.6 in) | about 190 g (6.7 oz) | Hearing developing |
| 19 | 2nd | a mango | about 15.3 cm (6 in) | about 240 g (8.5 oz) | Vernix and lanugo forming |
| 20 | 2nd | a banana | about 25 cm (10 in) head to heel | about 300 g (10.6 oz) | Anatomy scan window |
| 21 | 2nd | a carrot | about 26.7 cm (10.5 in) | about 360 g (12.7 oz) | Movements more noticeable |
| 22 | 2nd | a papaya | about 27.8 cm (10.9 in) | about 430 g (15 oz) | Senses sharpening |
| 23 | 2nd | a grapefruit | about 28.9 cm (11.4 in) | about 500 g (1.1 lb) | Lots of REM sleep |
| 24 | 2nd | an ear of corn | about 30 cm (11.8 in) | about 600 g (1.3 lb) | Lungs keep developing |
| 25 | 2nd | a rutabaga (swede) | about 34.6 cm (13.6 in) | about 660 g (1.5 lb) | Responds to familiar voices |
| 26 | 2nd | a head of lettuce | about 35.6 cm (14 in) | about 760 g (1.7 lb) | Eyes begin to open |
| 27 | 2nd | a cauliflower | about 36.6 cm (14.4 in) | about 875 g (1.9 lb) | Last week of trimester two |
| 28 | 3rd | an eggplant (aubergine) | about 37.6 cm (14.8 in) | about 1 kg (2.2 lb) | Third trimester begins |
| 29 | 3rd | a butternut squash | about 38.6 cm (15.2 in) | about 1.15 kg (2.5 lb) | Rapid weight gain |
| 30 | 3rd | a cabbage | about 39.9 cm (15.7 in) | about 1.3 kg (2.9 lb) | Bone marrow makes blood cells |
| 31 | 3rd | a coconut | about 41.1 cm (16.2 in) | about 1.5 kg (3.3 lb) | Major development largely done |
| 32 | 3rd | a squash | about 42.4 cm (16.7 in) | about 1.7 kg (3.75 lb) | Practising breathing |
| 33 | 3rd | a pineapple | about 43.7 cm (17.2 in) | about 1.9 kg (4.2 lb) | Skull stays soft |
| 34 | 3rd | a cantaloupe melon | about 45 cm (17.7 in) | about 2.1 kg (4.7 lb) | Lungs maturing |
| 35 | 3rd | a honeydew melon | about 46.2 cm (18.2 in) | about 2.4 kg (5.3 lb) | Space getting tight |
| 36 | 3rd | a romaine lettuce | about 47.4 cm (18.7 in) | about 2.6 kg (5.8 lb) | Baby may drop lower |
| 37 | 3rd | a bunch of Swiss chard | about 48.6 cm (19.1 in) | about 2.9 kg (6.3 lb) | Early term |
| 38 | 3rd | a leek | about 49.8 cm (19.6 in) | about 3.1 kg (6.8 lb) | Gaining fat |
| 39 | 3rd | a small watermelon | about 50.7 cm (20 in) | about 3.3 kg (7.3 lb) | Full term |
| 40 | 3rd | a small pumpkin | about 51.2 cm (20.2 in) | about 3.4 kg (7.6 lb) | Due date week |
First trimester: weeks 1 to 13
This is when the most dramatic development happens, even though there's little to see from the outside. By the end of week 8, ACOG notes the embryo is about half an inch long and the heart, brain and spine have begun to form. From week 11 your baby is called a fetus. By the end of week 12, the fetus is about 2 inches long.
What you may feel: the NHS says early symptoms usually start around 4 to 6 weeks. Common ones include tiredness, nausea or vomiting (at any time of day), sore breasts, needing to pee more often, and a sensitive sense of smell. Some people have very few symptoms, which is also normal.
Key appointments: first prenatal or booking visit (often 8 to 12 weeks) and a dating scan around 11 to 14 weeks, where screening tests are usually offered.
Start here: 4 weeks · 8 weeks · 12 weeks. For symptom detail, see early pregnancy symptoms.
Second trimester: weeks 14 to 27
Many people find the second trimester the easiest stretch. Nausea often fades and energy returns. Your baby's bones harden, hearing develops (ACOG says a fetus can hear sounds around week 18), and by the end of week 24 your baby is about 12 inches long.
What you may feel: a growing bump, round ligament pain, a stuffy nose, heartburn, and the first flutters of movement. The NHS says most people feel movement between 16 and 24 weeks.
Key appointments: the mid-pregnancy anatomy scan at about 18 to 22 weeks, and glucose screening for gestational diabetes at about 24 to 28 weeks.
Start here: 16 weeks · 20 weeks · 24 weeks.
Third trimester: weeks 28 to 40
Your baby gains weight fast, practises breathing movements and, in most cases, settles head-down. ACOG says the fetus is nearly 15 inches long and about 2.5 pounds by the end of week 28, and about 20 inches and 7.5 to 8 pounds at 40 weeks.
What you may feel: tiredness again, breathlessness, back pain, broken sleep and Braxton Hicks contractions. The NHS advises going to sleep on your side from 28 weeks.
Key appointments: visits become more frequent, often every two weeks and then weekly from about 36 weeks. See our pregnancy appointment schedule.
Movements matter most now. Get to know your baby's usual pattern. If movements slow down, stop or change, call your midwife or maternity unit straight away, even at night. Our guide to when to start kick counts explains the different approaches.
Start here: 28 weeks · 32 weeks · 36 weeks · 40 weeks.
Free tools for every stage
| Tool | Useful from | What it does |
|---|---|---|
| Due date calculator | Positive test | Estimates your due date from your last period, conception or IVF transfer |
| How many weeks pregnant am I? | Any time | Shows your exact week, day and trimester |
| Online kick counter | Third trimester, or when advised | Times how long 10 movements take |
| Online contraction timer | Late pregnancy and labor | Logs how long contractions last and how far apart they are |
Follow your pregnancy week by week in Momi
The Momi app follows your pregnancy week by week. Its home screen shows a progress ring with the weeks to go and your baby's size, and each week has baby development updates and tips. You can also keep a Mom's and Dad's diary, a weekly bump photo journal, your weight log, appointments with medicine reminders, a kick counter and a contraction timer, all in one place.
Download Momi free on the App Store or Google Play. Free with ads; optional Premium adds a timeline you can export as a PDF journey book.
Sources
- ACOG, Changes During Pregnancy
- NHS Best Start in Life, Week-by-week guide to pregnancy
- Mayo Clinic, Fetal development: the first trimester
- NHS, Your baby's movements
- ACOG Committee Opinion No. 700, Methods for Estimating the Due Date
Medical disclaimer: Momi and this website provide general information, not medical advice. Always talk to your doctor or midwife; in an emergency call your local emergency number.
FAQ
How do I calculate my pregnancy week by week?
Count the full weeks from the first day of your last period to today. If your period started 10 weeks and 3 days ago, you are 10 weeks and 3 days pregnant, also written 10+3. Once you have a dating scan, count from the due date your provider gives you instead.
What size is my baby week by week?
On average your baby is about the size of a poppy seed at 4 weeks, a lime at 12 weeks, a banana at 20 weeks, an eggplant at 28 weeks and a small pumpkin at 40 weeks. The chart on this page lists every week with length and weight.
Why does pregnancy week by week start before I conceived?
Pregnancy is dated from the first day of your last period, because that date is easier to know than the day of conception. As a result, weeks 1 and 2 happen before you conceive, and a 40-week pregnancy includes about 38 weeks of your baby's growth.
When are the three trimesters?
The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth. Some sources round these slightly differently.
How much weight gain is typical week by week?
It depends on your weight before pregnancy, so there is no single weekly number. Most gain is in the second and third trimesters. Your doctor or midwife can tell you what range suits you, and Momi's weight tracker lets you log it over time.
When will I feel my baby move?
The NHS says most people first feel movement between 16 and 24 weeks, and after 20 weeks in a first pregnancy. Tell your midwife if you haven't felt any movement by 24 weeks, and call straight away if movements slow down or change later on.
Related guides
Track this in Momi
Momi is a free pregnancy tracker app for iPhone and Android that follows pregnancy week by week, estimates the due date, and keeps a pregnancy journal, weight log, kick counter and contraction timer in one place.
