Trimester Calculator
Find out which trimester of pregnancy you are in and see key milestones.
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Result
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Formula
Calculates the current phase of pregnancy based on LMP or Due Date.
Worked Example
Understanding Pregnancy Trimesters
- First Trimester (Weeks 1 to 12): Foundation and organogenesis phase.
- Second Trimester (Weeks 13 to 26): Rapid growth and observable movement phase.
- Third Trimester (Weeks 27 to 40+): Final development and preparation for birth.
- Each trimester brings unique physical changes and nutritional needs.
While the 40-week timeline is standard, individual pregnancies can vary.
You can also calculate changes using our Pregnancy Due Date Calculator, Gestational Age Calculator or Pregnancy Weight Gain Calculator.
Frequently Asked Questions
When does the first trimester end?
The first trimester typically ends at the completion of week 12.
Which trimester is the longest?
Technically, all three are approximately the same length (13-14 weeks), though the third trimester can feel longer as you approach the due date.
What is the "fourth trimester"?
The "fourth trimester" refers to the three-month period immediately following birth, focusing on postpartum recovery and the baby's adjustment to life outside the womb.
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