Trimester Calculator: Find Your Pregnancy Length Based On LMP Date

Pregnancy is an amazing journey — a time when both the body and mind go through profound changes. During this journey, it’s important to know which trimester you’re in. This not only helps you understand your baby’s development, but also helps you better plan for your health, doctor’s appointments, and upcoming stages.

Our free and accurate trimester calculator helps you.
At LMP Calculator.com, we provide a reliable, medically reviewed tool that determines the current stage of your pregnancy based on your last menstrual period date (LMP) — just like your doctor does.

Enter your LMP date and find out in seconds:

✅ Which trimester you’re in
✅ Your pregnancy length (weeks and days)
✅ Estimated due date (EDD)

Why use Trimester Calculator?

Pregnancy is divided into three main stages — the first, second and third trimesters, each of which lasts for around 13-14 weeks. Knowing which stage you are in helps you to:

• Understand your baby’s development
• Plan antenatal checkups and appointments
• Manage pregnancy symptoms
• Track your health better

Our tool provides a simple, quick and reliable way to understand the progress of your pregnancy without any stress.

How does the trimester calculator work?

Our calculator is based on Naegele’s Rule, the accepted standard in the medical field for calculating pregnancy:

Due date = LMP date + 280 days (40 weeks)

It then automatically calculates:

📅 How many weeks and days pregnant you are
🤰 What trimester you are currently in
📆 Estimated due date
📊 Week-by-week analysis of pregnancy progress

Only one thing is needed — the date of your last menstrual period. No ultrasound, no records — just your memory or calendar.

💡 Tip: If you don’t remember the LMP, check your mobile app, calendar or notes.

Understand the three trimesters of pregnancy

🌱 First trimester (weeks 1 to 12)

This is the stage when miraculous changes begin in your body. During this time, the major organs of the baby start forming.

Key milestones:

Menstruation stops and pregnancy test comes out positive
Morning sickness

Baby’s heart starts beating by the 6th week

Development of the nervous system, heart, eyes and other organs
First prenatal checkup

What to do:

• Take prenatal vitamins containing folic acid
• Avoid alcohol, smoking and raw meat
• Get good sleep
• Eat small meals

Our calculator will tell you if you are in this crucial early stage, so you can adopt healthy habits in time.

🌞 Second trimester (weeks 13 to 26)

This is often called the “golden period”. Energy returns, the baby’s first movements are felt and the baby bump begins to appear.

Key milestones:

• Feeling baby’s kicks (18-22 weeks)
• Anatomy scan reveals baby’s sex
• Skin and hair start to glow
• Start attending antenatal classes
• Continue regular doctor’s checkups

What to do:

• Start gentle exercise like yoga or walking
• Plan the nursery
• Start preparing for labour
• Keep an eye on baby’s movements

If the calculator shows the second trimester, celebrate — this is the most joyous stage of pregnancy!

🌙 Third trimester (week 27 to delivery)

The final stage! Baby gains weight rapidly and is ready for birth.

Key milestones:

• Baby gaining weight rapidly
• Braxton Hicks contractions (not true prenatal contractions)
• Baby descending into the pelvis (lightening)
• Frequent doctor check-ups (every 1-2 weeks)
• Prepare hospital bag

What to do:

• Practice breathing techniques
• Create a birth plan
• Get as much rest as possible
• Count baby’s movements daily (kick counter)
• When the calculator shows the third trimester, know it — your baby could come any day!

Why choose our trimester calculator?

There are many pregnancy apps and tools on the internet, but why trust our tool?

✅ Reviewed by medical experts – based on advice from gynaecologists and midwives
✅ Accurate and reliable – based on Negels Rule and international standards
✅ Easy interface – simple, clear and mobile friendly
✅ PDF download feature – save your results and share with your doctor
✅ No ads, no login – completely private and free

We believe every woman has the right to clear, reliable and easy information during pregnancy.

How to use Trimester Calculator?

(3 easy steps)

• Enter the LMP date

• Select your last menstrual period date from the calendar.

• Click on “Calculate Trimester”

• The results will be displayed instantly.

• Save your report in PDF

• Download a professional report by clicking on the “Save to PDF” button.

📁 Ideally to carry while visiting the doctor!

Frequently Asked Questions (FAQ)

Disclaimer: The information provided by Trimester Calculator is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your doctor or qualified health provider with any questions or concerns.