Find your current trimester and see key dates for all three trimesters. Enter your LMP to view trimester start and end dates.
Pregnancy is divided into three trimesters, each lasting approximately 13-14 weeks. Understanding which trimester you are in helps you anticipate fetal development milestones, schedule prenatal screenings, and prepare for the physical changes that come with each stage.
The first trimester (weeks 1-12) is when the embryo's major organs form and the risk of miscarriage is highest. The second trimester (weeks 13-27) is often called the "golden period" — morning sickness fades, energy returns, and you may start feeling the baby move. The third trimester (weeks 28-40) is the home stretch, with rapid fetal growth and preparation for delivery.
This calculator shows you exactly which trimester you are in, how far along you are within that trimester, and the exact dates each trimester begins and ends based on your LMP. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Knowing your trimester is essential for understanding which prenatal tests are due, what symptoms to expect, and how your baby is developing. Employers, insurance companies, and maternity leave policies also reference trimesters. This tool gives you instant clarity and helps you plan each phase of your pregnancy. Having a precise figure at your fingertips empowers better planning and more confident decisions.
T1: Week 1 (LMP) through Week 12, Day 6 T2: Week 13, Day 0 through Week 27, Day 6 T3: Week 28, Day 0 through Week 40, Day 0 (EDD) GA weeks = floor((today − LMP) / 7)
Result: 1st Trimester — Week 10
With an LMP of December 1, 2025, and today being February 9, 2026, you are at 10 weeks and 1 day — firmly in the first trimester. The first trimester ends on February 22, 2026 (end of week 12). The second trimester runs from February 23 to June 7, and the third from June 8 to September 7.
Weeks 1-12 are a period of incredibly rapid development. By week 5, the heart begins beating. By week 8, all major organ systems are present in basic form. By week 12, the fetus has fingers, toes, and can make tiny movements. Prenatal vitamins with folic acid are critical during this time to prevent neural tube defects.
Weeks 13-27 bring visible growth and exciting milestones. Around week 16-20, many women feel the first fetal movements. The anatomy scan around week 20 provides a detailed look at the baby's development. Gender can often be determined during this scan.
Weeks 28-40 focus on maturation and weight gain. The baby's lungs mature, fat stores develop, and brain growth accelerates. Third trimester prenatal visits monitor fetal position, growth, and maternal health as delivery approaches.
The first trimester ends at the completion of week 12 (12 weeks, 6 days). Week 13 marks the start of the second trimester. This timing is standardized by ACOG.
For most women, morning sickness subsides, energy levels return, and the belly is not yet large enough to cause significant discomfort. It is also when you may first feel the baby move (quickening), typically between 16-22 weeks.
The third trimester begins at week 28 (28 weeks, 0 days) and lasts until delivery, typically around week 40. This is the period of most rapid fetal growth — the baby roughly doubles in weight.
Not exactly. The first trimester is 12 weeks and 6 days, the second is 15 weeks, and the third is approximately 12 weeks (28-40). The second trimester is the longest by a few weeks.
Yes. First trimester: nuchal translucency scan, NIPT, blood work. Second trimester: anatomy scan, glucose screening. Third trimester: Group B strep test, non-stress tests if needed. Timing is based on gestational weeks.
Babies born at 37-38 weeks are considered early term, 39-40 weeks full term, and 41+ weeks late term. Premature birth before 37 weeks may require specialized care. The third trimester is critical for lung and brain development.