Pregnancy Week Calculator
How many weeks pregnant are you? See your week, trimester and month, how big your baby is this week, and what usually comes next.
A longer cycle usually means you ovulated later, so you're a little less far along. The luteal phase (ovulation to next period) is usually 14 days.
Counts a day-5 embryo (blastocyst). Switch to Advanced for day 3 or day 6.
Today by default. Pick a past or future date to see how far along you were or will be.
Week-by-week guide with your dates
How your pregnancy week is worked out
Count the days from day 0, then split them into whole weeks and days.
- 1
Find day 0
10 August 2026
first day of last period - 2
Count the days
19 October 2026 − day 0
= 70 days - 3
Split into weeks
70 ÷ 7 = 10 r 0
= 10w 0d - 4
Where you are
First trimester
Month 3 · 25%
Read more: the formula, a worked example, baby sizes and typical milestones
Pregnancy is counted in weeks from the first day of your last period ("day 0"), about two weeks before you conceive. That's why you're already "4 weeks pregnant" around the time you miss a period. A full pregnancy is counted as 40 weeks (280 days) from day 0.
The formula
days pregnant = date you're checking − day 0
weeks pregnant = whole weeks in those days, plus the days left over
days to go = 280 − days pregnant
Day 0 depends on what you know:
| You know | Day 0 is |
|---|---|
| First day of your last period | that day, + (cycle − 28) − (luteal phase − 14) |
| Your due date | due date − 280 days |
| Conception date | conception − 14 days |
| IVF transfer, day 3 / 5 / 6 embryo | transfer − 17 / 19 / 20 days |
| A scan | scan date − days pregnant at the scan |
"10 weeks 0 days pregnant" means 10 whole weeks have passed, so you're in your 11th week. Week-by-week guides and baby sizes on this page use whole weeks (10w 0d to 10w 6d is "10 weeks").
Worked example
Your last period started on 1 August 2026 and your cycle is 28 days, so day 0 is 1 August 2026. Checking on 10 October 2026: 30 days (rest of August) + 30 (September) + 10 (October) = 70 days. 70 ÷ 7 = 10 with 0 left over, so you're 10 weeks 0 days pregnant, in week 11. That's the first trimester (up to 13w 6d) and month 3 (weeks 9 to 13). Days to go: 280 − 70 = 210, and 70 ÷ 280 = 25% of the way. Your estimated due date is 1 August 2026 + 280 days = Saturday 8 May 2027. At 10 weeks your baby is roughly the size of a kumquat: about 3.1 cm (1.2 in) from head to bottom and about 4 g (0.1 oz).
Trimesters and months
| Stage | Weeks pregnant |
|---|---|
| First trimester | 0w 0d – 13w 6d |
| Second trimester | 14w 0d – 27w 6d |
| Third trimester | 28w 0d – birth |
| Month 1 | week 1 – 4 |
| Month 2 | week 5 – 8 |
| Month 3 | week 9 – 13 |
| Month 4 | week 14 – 17 |
| Month 5 | week 18 – 22 |
| Month 6 | week 23 – 27 |
| Month 7 | week 28 – 31 |
| Month 8 | week 32 – 35 |
| Month 9 | week 36 – 40+ |
Months are only a rough guide (40 weeks doesn't split evenly into 9 months, and sources differ by a week or so). Doctors and midwives count in weeks.
Baby size by week
Approximate average sizes. Up to 19 weeks the length is measured from head to bottom; from 20 weeks it's head to heel, which is why it jumps at 20 weeks. The fruit and veg are only a fun way to picture it.
| Weeks | About the size of | Length | Weight |
|---|---|---|---|
| 4 | a poppy seed | 1 mm | under 1 g |
| 5 | a sesame seed | 2 mm | under 1 g |
| 6 | a lentil | 6 mm | under 1 g |
| 7 | a blueberry | 1.3 cm | 1 g |
| 8 | a raspberry | 1.6 cm | 1 g |
| 9 | a cherry | 2.3 cm | 2 g |
| 10 | a kumquat | 3.1 cm | 4 g |
| 11 | a fig | 4.1 cm | 7 g |
| 12 | a lime | 5.4 cm | 14 g |
| 13 | a lemon | 7.4 cm | 23 g |
| 14 | a peach | 8.7 cm | 43 g |
| 15 | an apple | 10.1 cm | 70 g |
| 16 | an avocado | 11.6 cm | 100 g |
| 17 | a pear | 13 cm | 140 g |
| 18 | a sweet potato | 14.2 cm | 190 g |
| 19 | a mango | 15.3 cm | 240 g |
| 20 | a banana | 25.6 cm | 300 g |
| 21 | a carrot | 26.7 cm | 360 g |
| 22 | a papaya | 27.8 cm | 430 g |
| 23 | a grapefruit | 28.9 cm | 500 g |
| 24 | an ear of corn | 30 cm | 600 g |
| 25 | a cauliflower | 34.6 cm | 660 g |
| 26 | a lettuce | 35.6 cm | 760 g |
| 27 | a cabbage | 36.6 cm | 875 g |
| 28 | an aubergine (eggplant) | 37.6 cm | 1,000 g |
| 29 | a butternut squash | 38.6 cm | 1,150 g |
| 30 | a large cabbage | 39.9 cm | 1,320 g |
| 31 | a coconut | 41.1 cm | 1,500 g |
| 32 | a squash | 42.4 cm | 1,700 g |
| 33 | a pineapple | 43.7 cm | 1,920 g |
| 34 | a cantaloupe melon | 45 cm | 2,150 g |
| 35 | a honeydew melon | 46.2 cm | 2,380 g |
| 36 | a romaine lettuce | 47.4 cm | 2,620 g |
| 37 | a bunch of chard | 48.6 cm | 2,860 g |
| 38 | a leek | 49.8 cm | 3,080 g |
| 39 | a small watermelon | 50.7 cm | 3,290 g |
| 40 | a small pumpkin | 51.2 cm | 3,460 g |
| 41 | a watermelon | 51.5 cm | 3,600 g |
| 42 | a large pumpkin | 51.7 cm | 3,690 g |
Milestones
The checks and tests on this page are typical across many countries, but which ones you're offered and when depends on where you live, your clinic and your health. Your midwife or doctor will tell you your own schedule.
For information only, not medical advice. This calculator can't tell you whether a pregnancy is healthy. If you have pain, bleeding, fewer baby movements or any worry, contact your midwife, doctor or local emergency number straight away. Checked on 10 October 2026.
Common questions
How do I work out how many weeks pregnant I am?
Count the days from the first day of your last period (day 0) to today, then divide by 7. The whole weeks are your weeks pregnant and the days left over are the extra days. For example, 70 days is 10 weeks 0 days. If you know your due date, day 0 is 280 days before it.
Why am I already 4 weeks pregnant when I've just missed a period?
Pregnancy is counted from the first day of your last period, about two weeks before you conceive. That's why you're already "4 weeks pregnant" around the time you miss a period, even though conception happened only about two weeks earlier.
If I'm 10 weeks pregnant, which week am I in?
"10 weeks 0 days pregnant" means 10 whole weeks have passed, so you're in your 11th week. Week-by-week guides and baby sizes use whole weeks, so anything from 10 weeks 0 days to 10 weeks 6 days counts as "10 weeks".
When does each trimester start?
The first trimester runs from 0 weeks to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days until birth. Doctors and midwives count in weeks rather than months, because 40 weeks doesn't split evenly into 9 months.
How many weeks is a full pregnancy?
A full pregnancy is counted as 40 weeks, or 280 days, from the first day of your last period. Days to go are 280 minus the days you're already pregnant, so at 70 days you have 210 days to go and you're 25% of the way.
How big is my baby this week?
The calculator shows an approximate average size for your week, compared with a fruit or vegetable. Up to 19 weeks the length is measured from head to bottom; from 20 weeks it's head to heel, which is why it jumps at 20 weeks. At 10 weeks a baby is roughly the size of a kumquat.
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