Updated June 17, 2026
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Full-term pregnancy is defined as 39 weeks 0 days to 40 weeks 6 days. Births from 37 to 42 weeks are all within the normal delivery range, but 39 to 40 weeks is considered optimal because important development, particularly brain and lung maturity, continues in those final weeks.
The official ACOG gestational age categories
| Category | Weeks of gestation |
|---|---|
| Preterm | Before 37 weeks |
| Early term | 37 weeks 0 days to 38 weeks 6 days |
| Full term | 39 weeks 0 days to 40 weeks 6 days |
| Late term | 41 weeks 0 days to 41 weeks 6 days |
| Post term | 42 weeks and beyond |
These categories from the American College of Obstetricians and Gynecologists (ACOG) replaced older, looser definitions of "term" precisely because research showed that outcomes for babies born at 37 or 38 weeks are meaningfully different from those born at 39 to 40 weeks.
Why does the last week matter so much?
Between 37 and 40 weeks, the baby's brain grows significantly, the lungs continue to mature, and the liver accumulates stores needed for life outside the womb. Babies born at 37 or 38 weeks (early term) are more likely to need extra support with breathing, feeding, and temperature regulation than babies born at 39 to 40 weeks, even though both are technically "at term" by the older definition.
Is 37 weeks considered full term?
By modern ACOG definitions, 37 weeks is early term, not full term. Before 2013, 37 weeks was called "term," but updated guidelines distinguish early term (37 to 38 weeks) from full term (39 to 40 weeks) because outcomes differ. A healthy birth at 37 weeks is common and usually fine, but it is not identical to birth at 39 to 40 weeks in terms of developmental readiness.
What happens after 40 weeks?
Going past 40 weeks is common and not inherently dangerous, but providers typically monitor the placenta and fetal wellbeing more closely after 40 weeks. Most will discuss induction options between 41 and 42 weeks because the risk of placental aging (post-maturity) rises after 42 weeks. The Due Date Calculator shows exactly where you are in this window. See also how accurate a due date really is and whether going "overdue" is meaningful for your situation.
Every pregnancy is different. Discuss your gestational age, birth timing, and any concerns about early or late delivery with your doctor or midwife. They are best placed to advise you based on your specific clinical picture.
Find your due date
Get your estimated due date and current week in seconds.