PREGNANCY weeks, months and trimesters explained

Trying to figure out what week, month and trimester you are in your pregnancy can be confusing. Check out the chart and commonly asked questions below to help make things crystal clear.

Why is pregnancy counted from the start of my last period?

Even though you weren’t pregnant on the first day of your last menstrual period (LMP) – that is the date from which your Lead Maternity Caregiver (LMC) will start counting.

The first day of your LMP is usually about two weeks before you ovulated and conceived your baby. It’s counted from this date because most women don't know exactly when they ovulated, but most of them do know when their last period started.

How is my due date calculated?

Your due date is calculated as 280 days from the first day of your period, this is exactly 40 weeks. However, your due date is just an estimate, only 5 percent of babies are actually born on their due date.

Find out when your baby is due by using our Due Date Calculator .

How long is a trimester?

Trimesters are generally about three months each. The first trimester being from weeks 0-13, second trimester weeks 14- 27 and third trimester from week 28 onwards.

Is pregnancy really nine months long?

This is a tricky one as it’s not exactly nine months and it varies based on when baby is actually born, but it’s generally nine months and one week – or longer if you are overdue. Read this great article on why pregnancy is nine months here.


How do I know how many months pregnant I am?

Check out the chart below to work out how many months pregnant you are.

  • Click here for a free printable version of this chart  below: trimester guide.



Pregnancy _Web _Week _Month _Trimester _OHbaby _LR


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