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How Long Is Pregnancy: Days, Weeks, Months, Trimesters

The average human pregnancy is 40 weeks long. However, a pregnancy is considered term between 37 weeks and 41 weeks 6 days. Babies born on or before 36 weeks 6 days are consider preterm or premature. Babies born between 37 weeks and 38 weeks 6 days are considered early term. Babies born between 39 weeks and 40 weeks 6 days are considered full term. Babies born between 41 weeks and 41 weeks 6 days. Babies born on or after 42 weeks are consider post-term or post-date. (Note: Prior to October 2013, babies were considered term between week 37 and week 42 of gestation.)

To calculate the length of your pregnancy, begin with the date of ovulation. The two weeks prior to ovulation are considered weeks 1 and 2 of pregnancy. For women who ovulate on day 14 of the menstrual cycle, day 1 of pregnancy will correspond with day 1 of the last menstrual period (LMP).

Pregnancy can be broken down into days, weeks, months and trimesters. Day 1 marks the beginning of week 1 of pregnancy, month 1 of pregnancy, and the start of the first trimester. A baby is conceived during week 3 of pregnancy. Day 15 marks the beginning of the week 3. The average pregnancy is 280 days long.

Weeks and Days of Pregnancy

Another way to talk about the days and weeks of pregnancy is to combine the two units of measurement. Week 1 of pregnancy begins on 0 weeks 1 day and ends on 1 week 0 days of pregnancy. Week 2 of pregnancy encompasses the time between 1 week 1 day and 2 weeks 0 days of pregnancy. A baby born on 38 weeks 3 days of pregnancy is born during week 39 of pregnancy.

Although most health care providers will take about the length of pregnancy in terms of weeks, the weeks of pregnancy can also be combined into months. Because some months are longer than others, some months consists of 4 weeks while others consist of 5 weeks. The average pregnancy is 9 months long. (Click on the calendar to view the full size of the image.)

Weeks, Months, and Trimesters of Pregnancy

Pregnancy can also be broken down into trimesters. The first three months of pregnancy comprise the first trimester. Months 4, 5, and 6 comprise the second trimester. The third trimester consists of months 7, 8, and 9 of pregnancy.

In addition to the days of pregnancy, the length of a pregnancy can also be determined by calculating the days post ovulation (DPO). Day 15 of pregnancy is also 1 DPO. The average pregnancy lasts 266 DPO.

Month 1 of Pregnancy

Month 2 of Pregnancy

Month 3 of Pregnancy

Month 4 of Pregnancy

Month 5 of Pregnancy

Month 6 of Pregnancy

Month 7 of Pregnancy

Month 8 of Pregnancy

Month 9 of Pregnancy

Month 10 of Pregnancy


Ob-Gyns Redefine Meaning of “Term Pregnancy”:
Pregnancy Length:

Image Credits

Weeks and Days of Pregnancy © 2012 Heather Johnson
Weeks, Months, and Trimesters of Pregnancy © 2012 Heather Johnson
Month 1 of Pregnancy © 2012 Heather Johnson
Month 2 of Pregnancy © 2012 Heather Johnson
Month 3 of Pregnancy © 2012 Heather Johnson
Month 4 of Pregnancy © 2012 Heather Johnson
Month 5 of Pregnancy © 2012 Heather Johnson
Month 6 of Pregnancy © 2012 Heather Johnson
Month 7 of Pregnancy © 2012 Heather Johnson
Month 8 of Pregnancy © 2012 Heather Johnson
Month 9 of Pregnancy © 2012 Heather Johnson
Month 10 of Pregnancy © 2012 Heather Johnson


  1. Irina David

    January 20, 2016 at 7:14 pm

    Good breakdown. . It can be confusing sometimes. . I’ve forwarded to my friend who’s struggling with her calculations. . 🙂

  2. mail4rosey

    January 20, 2016 at 7:21 pm

    That’s a nice break down sheet. It really can be a bit confusing.

  3. Rebecca Swenor

    January 20, 2016 at 8:57 pm

    This is a great reference for those women who are or who want to be pregnant. The charts are a great way to tell when your conception days are for those wanting to get pregnant. I will have to share this with my sister and my niece who have been thinking about having another child.

  4. Stefany @ ToBeThode

    January 20, 2016 at 9:21 pm

    This is great information for those pregnant! It can be a bit confusing at times.

  5. Pricilla

    January 21, 2016 at 3:14 pm

    There is a lot of great information here. I’m far too old to need it but I’m sure that those of childbearing age will find the charts very useful.

  6. Emily, Our house now a home

    January 21, 2016 at 3:43 pm

    This is so helpful to expecting women, I always thought it was odd that my pregnancy started counting technically before I conceived :/ Towards the end of the pregnancy it is all too long!

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