How pregnancy weeks convert to months β and why the numbers can be confusing
Pregnancy is 40 weeks β which most people assume is 10 months (40 Γ· 4 = 10). But the confusion comes from how we count months. Calendar months have 4β4.5 weeks (not exactly 4), so 40 weeks actually works out to about 9 months and 1 week. Pregnancy is officially described as nine months, with the tenth month being the final push to delivery.
| Pregnancy Week | Month | Trimester | Key Milestone |
|---|---|---|---|
| Weeks 1β4 | Month 1 | First Trimester | Conception, implantation, hCG rise |
| Weeks 5β8 | Month 2 | First Trimester | Heartbeat detected, organs forming |
| Weeks 9β13 | Month 3 | First Trimester | Fetus fully formed, miscarriage risk drops |
| Weeks 14β17 | Month 4 | Second Trimester | Anatomy scan, bump visible |
| Weeks 18β22 | Month 5 | Second Trimester | First movements felt, gender scan |
| Weeks 23β27 | Month 6 | Second Trimester | Baby gains weight, viability milestone at W24 |
| Weeks 28β31 | Month 7 | Third Trimester | Brain development, eyes open |
| Weeks 32β35 | Month 8 | Third Trimester | Lungs maturing, baby engaging in pelvis |
| Weeks 36β40 | Month 9 | Third Trimester | Full term at 37w, due date at 40w |
Doctors and midwives always refer to pregnancy in weeks, not months. When someone asks "how many weeks are you?" β this is the universally understood measure for tracking pregnancy.
Pregnancy weeks are counted from the first day of your last menstrual period (LMP) β not from conception. This means you're already technically "2 weeks pregnant" before you even conceive.
A baby is considered "full term" at 37 weeks and can safely be born without concern about prematurity. The due date is calculated at 40 weeks.
First trimester: weeks 1β13. Second trimester: weeks 14β26. Third trimester: weeks 27β40. The division into three trimesters helps doctors organize care and monitoring.
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