Pregnancy Trimester Calculator 2025: Weeks, Milestones, and Prenatal Care
Pregnancy is divided into three trimesters, each with unique fetal development and maternal changes. Our trimester calculator uses LMP or due date to show current trimester, weeks completed, and upcoming milestones.
Trimester Definitions
| Trimester | Weeks | Key Events |
|---|---|---|
| First | 0–12 | Implantation, organogenesis, NT scan |
| Second | 13–27 | Quickening, anatomy scan, GDM test |
| Third | 28–40 | Fetal growth, kick counts, cervical checks |
First Trimester (Weeks 1–12)
- Morning sickness peaks at 9 weeks
- Heart begins beating at 6 weeks
- NT scan at 11–13 weeks
- High miscarriage risk
Second Trimester (Weeks 13–27)
- Energy returns, belly grows
- Fetal movements felt ~18–20 weeks
- Anatomy scan at 18–20 weeks
- Glucose challenge at 24–28 weeks
Third Trimester (Weeks 28–40)
- Baby gains ½ lb/week
- Start kick counts at 28 weeks
- Group B Strep test at 35–37 weeks
- Monitor for preterm labor
Calculation Method
From LMP: GA = Today − LMP. EDD = LMP + 280 days.
From EDD: GA = 280 − (EDD − Today).
Step-by-Step Example
LMP: Feb 1, 2025. Today: May 15, 2025.
- Days since LMP = 103
- GA = 14 weeks 5 days
- Current: Second Trimester
- EDD = Nov 8, 2025
Accuracy Tips
- Use early ultrasound for dating
- Irregular cycles? Use EDD from scan
- IVF: EDD = transfer + 266 days
Prenatal Visit Schedule
- Every 4 weeks until 28w
- Every 2 weeks until 36w
- Weekly until delivery
Integration with Tools
FAQs
When does second trimester start? Week 13 (or end of week 12).
Can trimesters vary? Yes, some count 13–26 as second.
Post-term? >40 weeks. Induction often at 41.
Conclusion
Track your pregnancy journey with our 2025 Trimester Calculator. Know when to expect scans, tests, and baby’s growth spurts. Always follow your OB/GYN’s advice.
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