Pregnancy Trimester Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026
Disclaimer: This calculator is provided for informational and educational purposes only and does not constitute financial, medical, legal, or other professional advice. Always consult a qualified professional before making decisions based on these results.
How pregnancy is divided into trimesters
Trimester boundaries organize prenatal care scheduling, standard screening test timing, and typical symptom patterns into three roughly equal stages of pregnancy.
Worked example
At 20 weeks gestation:
Result = Second Trimester (weeks 13-26)
| Trimester | Weeks |
|---|---|
| First | 1-12 |
| Second | 13-26 |
| Third | 27 through delivery |
These boundaries are a widely used clinical convention, though the exact week cutoffs can vary slightly between different sources - this three-way split remains the most commonly cited version.