🤰 Trimester Calculator
Calculate your pregnancy trimester date ranges from your last menstrual period (LMP) or estimated due date (EDD). See which trimester you're currently in, track key milestones, and learn what to expect during each stage.
What Are Pregnancy Trimesters?
Pregnancy is divided into three trimesters, each roughly three months long. These divisions help healthcare providers track fetal development, schedule prenatal visits, and monitor for potential complications. The standard definitions used by the American College of Obstetricians and Gynecologists (ACOG) are:
- First Trimester: 0 weeks 0 days (LMP) to 13 weeks 6 days
- Second Trimester: 14 weeks 0 days to 27 weeks 6 days
- Third Trimester: 28 weeks 0 days until delivery
Pregnancy is dated from the first day of the last menstrual period (LMP), not from conception. Because ovulation typically occurs about two weeks after the LMP, gestational age is usually about 2 weeks ahead of fetal age.
First Trimester (Weeks 0–13)
The first trimester is a period of rapid development. The embryo's major organs — including the brain, heart, lungs, and liver — begin forming. By the end of this trimester, the embryo is officially called a fetus.
- Heartbeat detectable: Weeks 6–7
- First trimester screening: Weeks 11–14
- Common symptoms: Nausea, fatigue, breast tenderness, frequent urination
- Risk: Highest risk of miscarriage during this stage
Second Trimester (Weeks 14–27)
The second trimester is often called the "golden period" of pregnancy. Morning sickness and fatigue typically subside, and many women feel more energetic. This is when you'll start to feel the baby move (quickening).
- Quickening: Weeks 16–22
- Anatomy scan: Weeks 18–22
- Viability threshold: Week 24
- Common symptoms: Less nausea, more energy, visible bump
Third Trimester (Weeks 28–Delivery)
The third trimester is the final stretch. The baby gains weight rapidly, the lungs mature, and the body prepares for delivery. Prenatal visits become more frequent.
- Rapid weight gain begins: Week 31
- Group B strep test: Weeks 36–37
- Full term: Weeks 39–40
- Common symptoms: Back pain, Braxton Hicks contractions, shortness of breath
Why Use This Calculator?
- Exact date ranges: See the start and end dates for each trimester based on your LMP or EDD.
- Current progress: Know which trimester you're in today.
- Visual timeline: See your entire pregnancy at a glance with a color-coded timeline.
- Milestone tracking: Track key milestones and know what's coming next.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Trimester Calculator FAQ
What are the three trimesters of pregnancy?
The three trimesters are: First Trimester (0–13 weeks 6 days), Second Trimester (14 weeks 0 days–27 weeks 6 days), and Third Trimester (28 weeks 0 days until delivery).
How are trimesters calculated?
Trimesters are calculated from the first day of your last menstrual period (LMP). Each trimester is roughly 13–14 weeks long, dividing the 40-week pregnancy into three stages.
When does the second trimester start?
The second trimester starts at 14 weeks 0 days of gestation, which is the day after the first trimester ends (13 weeks 6 days).
When does the third trimester start?
The third trimester starts at 28 weeks 0 days of gestation.
What is the "golden period" of pregnancy?
The second trimester is often called the "golden period" because many of the uncomfortable symptoms of early pregnancy (nausea, fatigue) subside, and energy levels return.
What is quickening?
Quickening is the first time you feel your baby move. It typically occurs between 16 and 22 weeks of pregnancy, most commonly around 18–20 weeks for first-time mothers.
What is the viability threshold?
The viability threshold is the point at which a fetus can potentially survive outside the womb. It is generally considered to be around 24 weeks of gestation, though this can vary.
How accurate is this calculator?
This calculator uses ACOG trimester definitions and standard gestational age calculations. However, every pregnancy is unique. An early ultrasound (before 14 weeks) is the most accurate way to date a pregnancy. Always consult your healthcare provider.
Can I use this calculator for IVF pregnancy?
IVF pregnancies are dated differently — from the embryo transfer date, not the LMP. Your fertility clinic will provide a specific due date. This calculator is best for natural pregnancies.
Is this calculator free?
Yes, this calculator is completely free to use. No registration or personal data storage is required.