The second trimester usually starts around week 13 or 14 of pregnancy, depending on which medical definition you use.

Quick Scoop: When does the 2nd trimester start?

Most trusted pregnancy resources define trimesters slightly differently, but they all place the start of the second trimester just after week 12.

Here are the common definitions:

  • Some sources say the 2nd trimester runs from week 13 to the end of week 27.
  • Others, following ACOG-style definitions, count it from 14 weeks 0 days to 27 weeks 6 days.
  • Many hospital guides describe it simply as weeks 13 to 26.

In everyday use, most people and many clinics will tell you: once you hit 13 weeks, you’re in your second trimester.

Simple rule of thumb

  • If you just finished week 12: you’re entering the 2nd trimester.
  • By week 13: you’re safely considered in the 2nd trimester almost everywhere.

If your doctor uses a more technical definition, they might say it “officially” starts at 14 weeks 0 days, but functionally, week 13 is widely accepted as the start.

Always double-check with your own midwife or OB, because they may follow a specific guideline for dating your pregnancy.

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