Pregnancy Trimester Calculator

Pregnancy is split into three trimesters, each roughly three months long. Knowing which one you're in helps make sense of how you're feeling, what your baby is doing and what's coming up next in your care.

Our Pregnancy Trimester Calculator tells you which trimester you're in today and gives the exact start and end dates of all three. To see your due date and scan windows as well, try our main Pregnancy Calculator.

The three trimesters

On this site we use a common way of splitting pregnancy:

Some sources end the first trimester at 12 weeks instead of 13, so you may see slightly different dates elsewhere. It doesn't change your care, which is planned around your weeks of pregnancy rather than the trimester label.

Weeks are counted from the first day of your last period, so you're already about 2 weeks into the first trimester when you conceive.

How to use the calculator (Pregnancy Trimester Calculator)

1. Choose what to calculate from: your last period, your due date or your conception date.
2. Enter the date.
3. If you're using your last period, enter your average cycle length.

The calculator shows your current trimester, how many weeks pregnant you are, when the next trimester starts and a table of all three trimesters with their dates.

The first trimester (weeks 1 to 13)

Your baby's major organs start to form, and by the end of this trimester they're fully formed, although still very small. For many people, this is when sickness, tiredness and sore breasts are at their worst.

Your booking appointment with a midwife usually happens around 8 to 12 weeks, and your dating scan between 10 and 14 weeks.

The second trimester (weeks 14 to 27)

Many people find the second trimester the most comfortable. Sickness often eases, energy returns and your bump starts to show. You'll usually feel your baby move for the first time somewhere between 16 and 24 weeks.

Your anomaly scan, often called the 20-week scan, takes place between 18 and 21 weeks.

The third trimester (week 28 until birth)

Your baby gains most of their weight in the final trimester, and you'll probably feel more tired again as your bump grows. Antenatal appointments become more frequent, and it's a good time to think about your birth plan and maternity leave.

Your baby is considered full term at 37 weeks, and your due date is at 40 weeks. Our Pregnancy Countdown Calculator counts down the days.

A worked example

With the calculator's default settings, you'll see an example of someone 12 weeks pregnant. They're in the first trimester, and the second trimester starts in about 2 weeks. The table shows the start and end date of each trimester.