How many weeks pregnant am I?
Count from the first day of your last period: the number of full weeks since then is how many weeks pregnant you are. Enter your date below to get your exact weeks and days, month and trimester.
How pregnancy weeks are counted
Doctors and midwives count pregnancy in weeks, starting from the first day of your last menstrual period. Your baby is actually conceived about two weeks later, around ovulation. This means a full-term pregnancy is counted as 40 weeks, and you are already about 4 weeks pregnant when your period is late and a test turns positive.
If you have had a dating scan, use the due date from your scan, because it is more accurate than your period date. Enter it using the "Due date" option above.
Weeks, months and trimesters
| Month | Weeks | Trimester |
|---|---|---|
| 1st | 1 to 4 | First |
| 2nd | 5 to 8 | First |
| 3rd | 9 to 13 | First |
| 4th | 14 to 17 | Second |
| 5th | 18 to 22 | Second |
| 6th | 23 to 27 | Second |
| 7th | 28 to 31 | Third |
| 8th | 32 to 35 | Third |
| 9th | 36 to 40 | Third |
Because months have different lengths, pregnancy months never match weeks exactly. That's why doctors use weeks. Read what's happening in each week in our week-by-week guide, or see the month-by-month guide.
Questions about pregnancy weeks
How do I work out how many weeks pregnant I am?
Count the weeks from the first day of your last period to today. For example, if your last period started 10 weeks and 3 days ago, you are 10 weeks and 3 days pregnant, written 10+3. If you know your due date, subtract 280 days to find the start date and count from there.
Why am I already 4 weeks pregnant when I only just conceived?
Pregnancy is counted from the first day of your last period, which is usually about 2 weeks before you conceive. So when your period is due and a test turns positive, you are already counted as about 4 weeks pregnant.
How many months pregnant am I?
Pregnancy is about 9 months, or 40 weeks. Roughly: weeks 1 to 4 are month 1, 5 to 8 month 2, 9 to 13 month 3, 14 to 17 month 4, 18 to 22 month 5, 23 to 27 month 6, 28 to 31 month 7, 32 to 35 month 8 and 36 to 40 month 9.
What do 12+3 and similar numbers mean?
Doctors write pregnancy length as weeks plus days. 12+3 means 12 weeks and 3 days pregnant. You are in your 13th week.
Which trimester am I in?
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.