The second trimester usually runs from about week 13 or 14 of pregnancy up to the end of week 26 or 27, roughly covering months 4, 5, and 6 of pregnancy.

If you conceived naturally and count from the first day of your last menstrual period (how doctors usually date pregnancy), that means:

  • First trimester: up to 12–13 weeks.
  • Second trimester: about 13/14 weeks to 26/27 weeks.
  • Third trimester: starts around week 27/28 until birth.

Because different organizations use slightly different cutoffs, some say 13–26 weeks and others 14–27 weeks, but all place the second trimester squarely in the middle third of pregnancy.