Gestational age
Pregnancy is usually measured in completed weeks plus days — so 18+3 means 18 full weeks and 3 days since the first day of your last period.
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How many weeks pregnant am I?
Enter your last period or due date to calculate your current pregnancy week.
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How pregnancy weeks work
Trimesters
The first trimester runs to the end of week 13, the second from week 14 to 27, and the third from week 28 until birth.
When your dates change
If a scan gives you a new due date, switch to the Due date tab and enter it for the most up-to-date week.
FAQ
Questions parents ask
What does 18+3 mean?
It means 18 completed weeks and 3 days of pregnancy, counted from the first day of your last period.
How many weeks is a full-term pregnancy?
Pregnancy is often described as 40 weeks. Babies born from 37 weeks are generally considered term, and many are born between 37 and 42 weeks.
Is week 18 the same as 18 weeks?
People use both. Here, “18 weeks” means 18 completed weeks — you’re in the days after that milestone.