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Is pregnancy calculated from conception or last period?

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Many people mistakenly think pregnancy is calculated from conception or the date of their first missed period.

Pregnancy is actually tracked from the first day of your last period!

As a first time mom, you’ll want to learn all the details of the pregnancy timeline and what a first time mom needs to know.

Here are some easy pointers to start!

Positive pregnancy test on blue background.

Understanding Your Cycle and Conception

Each time a woman begins a menstrual cycle, her body is preparing for pregnancy.

According to, in a typical 28-day cycle, ovulation will occur on or about day 14, or within 4 days of the midpoint of a woman’s cycle.

Once a mature egg is released from the ovary, it has a lifespan of 12-24 hours for fertilization.

That may seem like a short window, but sperm can survive for several days to fertilize a mature egg. This widens the conception window to several days before ovulation to a few days post ovulation.

Implantation of a fertilized egg typically takes place 6-12 days from the time of ovulation. If an egg is not fertilized, it will disintegrate and shed along with the uterine wall and the cycle starts again.

You can learn more about early pregnancy signs here and when pregnancy symptoms start.

The 3 Stages of Pregnancy

As stated above, pregnancy starts from day one of a woman’s last menstrual cycle and continues through about 40 weeks or 9 months.

These 9 months are broken up into three trimesters, the first trimester, second and third.

Each pregnancy stage comes with unique challenges and experiences, some that are exciting and fun and others that aren’t!

Learn more about the three stages of pregnancy, here, and which one is the worst!


As a new mom, you’ll want to arm yourself with as much knowledge early on as you can.

As you get closer and closer to your due date, you’ll want to relax as you prepare for labor.

You can start by educating yourself about first time mom labor and typical postpartum body changes, and learn these easy newborn sleep tips.

You can find even more helpful tips for the first time mom in this growing archive, including the 3 first time mom books you can’t live without.