How many weeks is full term?
A pregnancy is considered full term from 39 weeks 0 days to 40 weeks 6 days. It’s a narrower window than the old “anytime after 37 weeks” — because those last couple of weeks turn out to matter quite a lot.
From early term to postterm
Tap a band to see what it means. Full term is the green stretch in the middle.
What “full term” means now
For a long time, any birth after 37 weeks was simply called “term.” That changed in 2013, when the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine introduced more precise labels — because research showed that important development continues right up to 39 weeks. The aim was partly to discourage non-medically-needed early deliveries.
Under the current definitions, full term is 39 0/7 to 40 6/7 weeks — that’s the green band in the explorer above, and the window generally regarded as best for an uncomplicated birth.
The full ladder, week by week
It helps to see the whole sequence. Anything before 37 weeks is preterm (premature). After that come the four “term” bands:
- Early term — 37 0/7 to 38 6/7 weeks
- Full term — 39 0/7 to 40 6/7 weeks
- Late term — 41 0/7 to 41 6/7 weeks
- Postterm — 42 0/7 weeks and beyond
So “early term” babies aren’t premature — they’ve passed 37 weeks — but they haven’t quite reached the full-term window either.
Why those last weeks matter
The difference between 37 and 39 weeks is bigger than it sounds. In those final weeks a baby’s brain grows substantially — at 35 weeks it weighs only around two-thirds of what it will at 39 — and the lungs and liver keep maturing. Babies also lay down fat that helps them regulate their temperature after birth. That’s why current guidance is to avoid inducing labour or scheduling a caesarean before 39 weeks unless there’s a medical reason.
Of course, plenty of healthy babies arrive early term, late term, or right on cue — every pregnancy is different, and the bands are guidance, not guarantees.
Common questions
This page shares general information, not medical advice. Every pregnancy is different — for anything about your own due date, delivery timing or health, your midwife or doctor is the right person to ask.
Sources
- American College of Obstetricians and Gynecologists (ACOG) & SMFM — 2013 “definition of term pregnancy” (early / full / late / postterm).
- March of Dimes & NIH (NICHD) — why at least 39 weeks is best, and late-pregnancy brain, lung and liver development.
Related
Thirty-nine to forty-one — a short, important stretch where a little extra time does a great deal of quiet work.