There are three trimesters in a typical pregnancy.

Quick Scoop: How many trimesters in a pregnancy?

For most full-term pregnancies, the journey is split into 3 main trimesters , each lasting about 12–14 weeks and together covering roughly 40 weeks of pregnancy.

  • First trimester: about weeks 1–13.
  • Second trimester: about weeks 14–27.
  • Third trimester: about weeks 28–40 (sometimes a bit beyond).

Some doctors and parents also casually talk about a “fourth trimester,” meaning the first 3 months after birth, but medically, pregnancy itself is divided into three trimesters.

Mini breakdown (weeks and phases)

  • A full-term pregnancy is usually around 40 weeks from the first day of the last menstrual period.
  • Each trimester comes with its own milestones and symptoms for both the pregnant person and the baby.

Simple HTML fact table

html

<table>
  <thead>
    <tr>
      <th>Trimester</th>
      <th>Approx. Weeks</th>
      <th>Notes</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>First trimester</td>
      <td>Weeks 1–13</td>
      <td>Early development; common time for nausea and fatigue [web:3][web:5]</td>
    </tr>
    <tr>
      <td>Second trimester</td>
      <td>Weeks 14–27</td>
      <td>Often called the “easier” middle phase; more visible growth [web:3][web:5][web:7]</td>
    </tr>
    <tr>
      <td>Third trimester</td>
      <td>Weeks 28–40+</td>
      <td>Baby gains most weight; body prepares for birth [web:3][web:5][web:7][web:9]</td>
    </tr>
  </tbody>
</table>

If you’re seeing people online mention a “fourth trimester,” they’re usually talking about the intense newborn period after birth — a recovery and bonding stage, not an official part of pregnancy.

TL;DR: A pregnancy is medically divided into 3 trimesters , each about 3 months long, with some people informally adding a “fourth trimester” for the first 3 months after birth.

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