What are the three trimesters of pregnancy?

The first trimester covers weeks 1–12, the second trimester weeks 13–26, and the third trimester weeks 27–40. Each trimester has distinct developmental milestones.

When is a baby considered full term?

A baby is considered full term at 37–42 weeks. Babies born before 37 weeks are preterm (premature). Born after 42 weeks is post-term.

When should I see a doctor to confirm my due date?

You should schedule your first prenatal appointment as soon as possible. A doctor may use ultrasound to confirm or adjust your due date, especially in the first 12 weeks.

Pregnancy Due Date Calculator

Estimate your baby's birth date from LMP or conception date

Health & Wellness | 40 weeks

Calculation Method

First day of your last menstrual period (LMP)

We add 280 days (40 weeks) to calculate your estimated due date.

Estimated conception date

We add 266 days (38 weeks) to calculate your estimated due date.

Estimated Due Date

Gestational Age

weeks & days

Trimester

Pregnancy Progress

Week 0 Week 20 Week 40

Key Milestones

Enter a date to get started

Select your last menstrual period date or conception date above to calculate your estimated due date.

How It Works

LMP Method: Adds 280 days (40 weeks) to the first day of your last period. This is the standard clinical approach.

Conception Method: Adds 266 days (38 weeks) to your estimated conception date for a direct calculation.

Trimester Guide

1st

First Trimester

Weeks 1–12 • Organ development

2nd

Second Trimester

Weeks 13–26 • Growth & movement

3rd

Third Trimester

Weeks 27–40 • Final development

Medical Disclaimer

This calculator provides an estimate only. Only about 5% of babies are born on their exact due date. Always consult your healthcare provider to confirm your due date.

How Pregnancy Due Date Calculation Works

Understanding the two most common methods doctors and calculators use to estimate your baby's arrival

Your estimated due date (EDD) — also called the estimated date of confinement (EDC) — is the date that is 40 weeks from the first day of your last menstrual period. This is based on Naegele's Rule, a formula developed in the early 19th century that remains the standard method used by obstetricians worldwide.

While no calculator can predict the exact date your baby will arrive, an accurate due date helps your healthcare provider monitor your pregnancy, schedule important screenings, and plan for delivery. Most babies are born within a window of two weeks before or after the estimated date.

LMP Method

The most widely used method. Add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle and ovulation on day 14.

Conception Method

If you know your conception date (e.g., from IVF or ovulation tracking), add 266 days (38 weeks) to estimate your due date with greater precision.

Ultrasound Dating

An early ultrasound (especially in the first 12 weeks) can confirm or adjust your due date by measuring the baby's size. This is the most accurate clinical method.

Key Pregnancy Milestones

Important dates and checkpoints to look forward to during your 40-week journey

12w

End of First Trimester — Week 12

The risk of miscarriage drops significantly after week 12. Your baby has all major organs formed and is about the size of a lime. Many parents choose to share their pregnancy news at this milestone. The nuchal translucency (NT) scan is typically performed around this time.

20w

Anatomy Scan — Week 20

The mid-pregnancy anatomy ultrasound (also called the anomaly scan or level 2 ultrasound) checks your baby's organs and development in detail. You may also find out your baby's sex at this scan. This is considered the halfway point of your pregnancy.

28w

Third Trimester Begins — Week 28

You enter the home stretch. Your baby's brain is rapidly developing, and they can now open their eyes and respond to light. Prenatal appointments become more frequent (typically every two weeks) to monitor growth and position. The glucose challenge test is usually done around weeks 24–28.

37w

Full Term — Week 37

Your baby is considered full term at 37 weeks. Babies born at this point have a very high chance of being healthy with no complications. Weekly check-ups begin, and your doctor will monitor for signs of labor. Your baby is settling into position in preparation for birth.

40w

Estimated Due Date — Week 40

Your calculated due date arrives! Remember, only about 5% of babies are born on their exact due date. If you pass 40 weeks, your doctor will continue to monitor you closely. Most providers will discuss induction of labor between 41 and 42 weeks to avoid risks associated with post-term pregnancy.

What to Expect Each Trimester

A quick guide to what you and your baby experience across the three stages of pregnancy

First Trimester (Weeks 1–12)

Morning sickness, fatigue, and frequent urination are common. Your baby's heart starts beating around week 6. Major organs and body structures form. An early ultrasound confirms the pregnancy and establishes a baseline due date.

Second Trimester (Weeks 13–26)

Often called the "golden trimester" — energy returns and nausea fades for most. You'll feel your baby move (quickening) around weeks 18–22. The anatomy scan provides a detailed look at your baby's development.

Third Trimester (Weeks 27–40)

Your baby grows rapidly and turns head-down in preparation for birth. Back pain, heartburn, and swelling are common. Braxton Hicks contractions may begin. Prenatal appointments increase to weekly visits as your due date approaches.

Prenatal Care Tips

Take prenatal vitamins with folic acid, attend all scheduled appointments, stay hydrated, eat a balanced diet, get moderate exercise, and avoid alcohol, smoking, and raw or undercooked foods throughout your pregnancy.

Frequently Asked Questions

Common questions about pregnancy due date calculation

The due date is an estimate. Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated due date. Factors such as irregular menstrual cycles, late ovulation, and individual baby growth rates can all affect accuracy. An early ultrasound scan (ideally before 12 weeks) is the most reliable way to confirm your due date.

The LMP (Last Menstrual Period) method calculates the due date by adding 280 days (40 weeks) to the first day of your last period. This is the most commonly used method and is based on Naegele's Rule. It assumes a standard 28-day menstrual cycle with ovulation occurring on day 14. If your cycle is longer or shorter than 28 days, your due date may need adjustment.

Pregnancy is divided into three trimesters: First trimester (weeks 1–12) covers early development when all major organs form. Second trimester (weeks 13–26) is often the most comfortable period, when fetal movement begins and the anatomy scan is performed. Third trimester (weeks 27–40) involves rapid growth and preparation for birth. Each trimester has distinct developmental milestones and common symptoms.

A baby is considered full term at 37–42 weeks of gestation. Babies born before 37 weeks are considered preterm (premature) and may need additional medical support. Babies born between 37 and 38 weeks and 6 days are "early term," while 39 to 40 weeks and 6 days is "full term." A birth after 42 weeks is considered post-term, and doctors typically recommend induction between 41 and 42 weeks.

You should schedule your first prenatal appointment as soon as you confirm your pregnancy, ideally within the first 8 weeks. A doctor may use ultrasound to confirm or adjust your due date, especially in the first 12 weeks when measurements are most accurate. Early prenatal care is important for monitoring your health and your baby's development from the very start.