How to Calculate Pregnancy Weeks & Trimesters

Pregnancy is an exciting time of rapid growth and change. The average pregnancy lasts 40 weeks, which is divided into three trimesters. During this time, your baby's body is developing, and your body is changing as well. Knowing which week and trimester of pregnancy you are in is very important for knowing whether you and the baby are developing as you should. You also can find interesting information about exactly how the baby is growing and changing week by week.

Instructions

• 1

  Mark the first day of your most recent menstrual period on a calendar.

• 2

  Count forward one week from this day to mark week one of your pregnancy. Continue this method of counting and mark each of the 40 weeks of your pregnancy.

• 3

  Mark the 12th week of your pregnancy as the end of your first trimester.

• 4

  Mark the beginning of the 13th week as the beginning of your second trimester, then mark the 28th week as the end of your second trimester

• 5

  Mark the beginning of the 29th week as the beginning of your third and final trimester. Then mark the end of the 40th week as the end of your third trimester, which should also be your due date.