Pregnancy is typically measured in weeks, months, and trimesters. Understanding how long pregnancy lasts and how it is divided helps expectant parents track fetal development and prepare for each stage of pregnancy.




How Long is a Full-Term Pregnancy?


A full-term pregnancy lasts about 40 weeks, starting from the first day of the woman’s last menstrual period (LMP). This is equivalent to approximately:


  • 9 months (though not exactly because months have varying lengths)


  • 3 trimesters (each lasting about 3 months)



However, some pregnancies may last a little shorter or longer, with normal full-term births occurring anywhere from 37 to 42 weeks.



Weeks to Months Breakdown


Pregnancy does not fit neatly into months since most months have 30 or 31 days, while pregnancy is counted in weeks. Below is a general guide for converting weeks into months:

Since a pregnancy does not start at conception but rather from the LMP, the first two weeks technically do not include fetal development but are included in the total count.


Understanding the Three Trimesters


Pregnancy is divided into three trimesters, each with unique developmental milestones.


First Trimester (Weeks 1 – 13)


Covers Months 1 to 3


This stage includes fertilization, implantation, and the early formation of major organs.


The first ultrasound is often done around weeks 6–8 to confirm pregnancy.


Morning sickness, fatigue, and hormonal changes are common.



Second Trimester (Weeks 14 – 27)


Covers Months 4 to 6


The baby’s movements (quickening) may be felt between 16-22 weeks.


The baby develops facial features, fingers, and hair.


The mother’s belly starts to show significantly.


A mid-pregnancy ultrasound is typically done between 18-22 weeks.



Third Trimester (Weeks 28 – 40)


Covers Months 7 to 9


The baby gains weight rapidly, and organs mature for birth.


Common symptoms include back pain, shortness of breath, and frequent urination.


Full-term is reached at 37 weeks, though labor can happen anytime between 37-42 weeks.




When is a Baby Considered Full-Term?


Early Term: 37 – 38 weeks


Full Term: 39 – 40 weeks


Late Term: 41 weeks


Post-Term: 42 weeks or later



Babies born after 39 weeks have the best chance of healthy development, though many are born earlier with proper medical care.



Final Thoughts


A full-term pregnancy lasts 40 weeks, or about 9 months, divided into 3 trimesters. Each stage of pregnancy brings different changes for both the mother and baby. Understanding the breakdown of weeks, months, and trimesters can help expectant parents track progress and prepare for a heal

thy birth.