How long does pregnancy last?
40 weeks, 9 months, 3 trimesters: how pregnancy length is actually calculated, and why the due date is only an estimate.
A full-term pregnancy lasts on average 40 weeks, or about 280 days, counted from the first day of your last period — not from conception, which usually happens about two weeks later.
This is why pregnancy is often described as '9 months,' even though 40 weeks actually adds up to a bit more than 9 calendar months. Pregnancy is also divided into 3 trimesters: the first runs from week 1 to about week 13, the second from week 14 to 27, and the third from week 28 until birth.
Your week, baby's size, your symptoms, your appointments and adapted menus, all in one app.
Download the app for free✨ Free to download — on phone, tablet and computer.
The estimated due date given by your healthcare provider is based on this 40-week average, adjusted if needed based on a first-trimester dating ultrasound, which is generally more accurate than a calculation based on your last period alone.
In practice, very few babies are born exactly on their due date. A birth between 37 and 42 weeks is considered full term. Before 37 weeks, it's called a premature (preterm) birth; after 42 weeks, your care team will typically monitor things more closely.
Sources
Photo: Unsplash
This information is general and does not replace advice from your healthcare professional (doctor, midwife, nurse, pharmacist). Every situation is unique: always check with them before making a decision. In an emergency, call 911 or your local emergency services.
