Pregnancy Week by Week
Find your pregnancy week from your last period or due date and see your baby’s size, development and the checks due each week.
About Pregnancy Week by Week
This free pregnancy week by week guide tells you how many weeks pregnant you are from the first day of your last period or your due date, and which trimester you are in. Step through any week from 1 to 42 to see what comes next.
For each week it shows your baby’s average length and weight, what is developing, and the usual scans, tests and care at that stage, such as the NT scan, anomaly scan and glucose test. It is general information to discuss with your doctor, and it runs in your browser.
How to use Pregnancy Week by Week
- Enter the first day of your last period, or your due date from a scan.
- See how many weeks and days pregnant you are and the trimester.
- Read your baby’s average size and what is developing this week.
- Step through the weeks to see what comes next.
Frequently asked questions
How are pregnancy weeks counted?
From the first day of your last menstrual period (LMP), not from conception. A full-term pregnancy is about 40 weeks (280 days) from the LMP. If an early scan gave a different due date, use the scan date.
How big is my baby this week?
Average sizes are shown: crown-to-rump length up to 19 weeks and crown-to-heel length from 20 weeks. Healthy babies vary a lot, and your scan report is the best guide to your own baby’s growth.
When are the main scans and tests?
Dating scan at 6–9 weeks, NT scan at 11–13 weeks, anomaly scan at 18–22 weeks, a sugar test at 24–28 weeks, and growth checks in the third trimester as your doctor advises.
How many weeks pregnant am I?
Count from the first day of your last period: the number of full weeks since then is your pregnancy week. Enter the date to see it with days.
How big is the baby at 20 weeks?
On average about 25 cm from crown to heel and about 300 g, though healthy babies vary.
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