Duration of Pregnancy

Duration of pregnancy

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How Do You Calculate the Weeks, Months and Trimesters of a Pregnancy?

Attempting to count the weeks of pregnancy can be quite daunting: It is calculated in weeks, months and trimesters - this system can seem confusing. This is how it works:


Overview: Weeks of Pregnancy, Months and Trimesters

A pregnancy is usually divided into weeks, months and trimesters. The following table gives you an overview of the counting methods:


Month of pregnancy

Week of pregnancy


1 1 - 4

2 5 - 8
3 9 - 12


4 13 - 16
5 17 - 20
6 21 - 24


7 25 - 28
8 29 - 32
9 33 - 36
10 37 - 40

Calculating Cut-Off Dates for an Abortion

Perhaps you are experiencing an unintended pregnancy and are faced with the decision of whether or not to abort.

While researching, you might have come across cut-off points of 6 or 22 weeks for a legal abortion. Sometimes the time limit of 63 days is given. It can be difficult to find your way through this confusion, especially when your thoughts and emotions are already tense and disoriented.

How to Calculate the Months

The months of pregnancy are divided into weeks and are calculated according to the lunar calendar. Here, each month consists of four weeks.

The first day of your last menstrual period (LMP) initiates the beginning of the first month; the fifth week is the beginning of the second month, etc.

  • Example: In which month of pregnancy are you at 17 weeks? Divide the 17 weeks by 4 weeks per month. The result is 4.25. This means that the 17th week of pregnancy is the start of the 5th month.

Calculating Weeks and Days

Besides calculating in weeks, months, and trimesters, there is also a more precise method, by counting in weeks and days.

Example: The last day of the 14th week can also be called 13 + 6.

This is how you calculate it: One week consists of 7 days. The first day of the 14th week is 13 + 0; the last day is 13 + 6. You continue by counting 14 + 0, which marks the beginning of the 15th week of pregnancy.

Unintended Pregnancy - Where Do I Go From Here?

So many unanswered questions are looming over you right now. This would be confusing and overwhelming. You do not have to walk this path alone! Our judgement-free resources were tailor-made for your situation:

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