The 3rd trimester of pregnancy usually starts around week 28 and lasts until birth, typically around week 40.

Quick Scoop

  • Most major medical sources say the third trimester begins at 28 weeks of pregnancy.
  • It continues until you deliver, which for many pregnancies is around 39–40 weeks, though some babies arrive a bit earlier or later.
  • In “months,” this roughly covers months 7, 8, and 9 of pregnancy.

Why the weeks sometimes differ

Some organizations or sites may say the third trimester starts at week 27 or at the beginning of week 29, but all are describing the same late‑pregnancy period when you’re in the final 3 months. Healthcare providers usually still treat 28 weeks as the standard marker.

Simple way to remember

  • Weeks 1–13: first trimester
  • Weeks 14–27: second trimester
  • Weeks 28–birth (around 40 weeks): third trimester

Always check with your own doctor or midwife, because they’ll base your exact timing and milestones on your personal due date and health.

Information gathered from public forums or data available on the internet and portrayed here.