How many weeks pregnant am I?
Pregnancy is counted from the first day of your last period, not from conception. Count the days since that date and divide by 7. If you know your due date, we count back from 40 weeks. Enter either one below.
Enter a date to calculate.
Everything is calculated on your own device. We store nothing and send nothing anywhere.
This is an estimate, not medical advice and not contraception. If in doubt, ask your GP or midwife.
How we calculate
A pregnancy lasts 40 weeks, counted from the first day of your last period. If you enter that date, we take your cycle length into account. If you enter your due date, we count back from 40 weeks.
The trimesters
The first trimester runs to 14 weeks, the second to 28 weeks and the third until birth.
Follow it week by week
In PERIOD. baby you follow your pregnancy week by week, with how big your baby is and what is happening.
Want to know every month, without the maths?
PERIOD. learns from your own cycles and keeps your predictions up to date. Free, no ads, and we never sell your data.
Frequently asked questions
When do pregnancy weeks start?
From the first day of your last period. That is why you are officially already about 2 weeks pregnant at conception.
How many weeks does a pregnancy last?
On average 40 weeks from the first day of your last period. Between 37 and 42 weeks counts as on time.
When does the second trimester start?
At around 14 weeks. The third trimester starts at around 28 weeks.
My scan says a different week, which is right?
Follow the scan: it is more accurate than counting from your last period.
Read more
Other free tools
Sources: NHS, Periods and fertility in the menstrual cycle; NHS, Pregnancy due date; ACOG, Methods for estimating the due date.