Pregnancy Due Date Calculator - Free Accurate Baby Birth Estimator
🤰 Pregnancy Tool

Pregnancy Due Date Calculator - Free Baby Birth Date Estimator

Calculate your baby's estimated due date instantly using your last menstrual period (LMP), conception date, or IVF transfer date. Get week-by-week pregnancy timeline, trimester breakdown, and key milestone dates.

🍼 Calculate Your Due Date

Enter your dates to estimate when your baby will arrive

Average Cycle Length: days
⚠️ Medical Disclaimer
This calculator provides an estimate only. Only about 5% of babies are born on their exact due date. Your healthcare provider will give you a more accurate date based on ultrasound measurements and other factors. Always consult with your doctor or midwife for medical advice.
🎀 Estimated Due Date
Select a date above

📖 How Pregnancy Due Date Calculation Works

Understanding how your due date is calculated helps you track your pregnancy journey and prepare for your baby's arrival. While the exact day of birth is unpredictable, these proven methods provide reliable estimates used by healthcare providers worldwide.

1

Naegele's Rule (LMP Method)

The most common method used by doctors. Add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. Formula: LMP + 280 days = Due Date. If your cycle is longer or shorter, the calculator adjusts accordingly.

2

Conception Date Method

If you know when you conceived (through ovulation tracking, fertility treatments, or specific circumstances), add 266 days (38 weeks) to that date. This is more accurate than LMP for those who track ovulation precisely.

3

IVF Transfer Calculation

For IVF pregnancies, the calculation is based on embryo transfer date. For Day 3 transfers, add 263 days. For Day 5 (blastocyst) transfers, add 261 days. This method provides the most accurate dating for assisted conception.

🗓️ Week-by-Week Pregnancy Timeline

Your 40-week pregnancy journey is divided into three trimesters, each with unique developments and milestones. Here's what to expect during each phase of this incredible transformation.

✨ Key Milestones Throughout Pregnancy
Weeks 1-4
🌱 Implantation & Early Development
Fertilized egg implants in the uterus. Pregnancy hormone (hCG) begins production. Many women don't yet know they're pregnant.
Weeks 5-8
💓 Heart Begins Beating
Baby's heart starts beating around week 6. Brain, spinal cord, and major organs begin forming. Morning sickness may begin.
Weeks 9-12
👶 Fetal Stage Begins
Baby is now officially a fetus. All major organs are formed. Fingers—and toes develop. First trimester screening available. Risk of miscarriage decreases significantly.
Weeks 13-16
🦴 Bones Begin Hardening
Second trimester begins—energy often returns. Baby can make facial expressions. Gender may be visible on ultrasound. Baby is about the size of an avocado.
Weeks 17-20
🦋 First Movements Felt
Many mothers feel first movements (quickening). Anatomy scan typically performed at week 20. Baby's hearing develops—they can hear your voice!
Weeks 21-24
✨ Viability Milestone
Baby reaches viability around week 24 with medical support. Lungs begin producing surfactant. Baby develops sleep-wake cycles. You may notice regular movement patterns.
Weeks 25-28
👀 Eyes Open
Third trimester begins. Baby's eyes open and respond to light. Brain develops rapidly. Glucose screening test typically performed. Baby weighs about 2-2.5 pounds.
Weeks 29-32
🧠 Rapid Brain Growth
Baby's brain triples in weight during this period. Bones fully develop but remain soft. Baby practices breathing movements. Most babies settle into head-down position.
Weeks 33-36
💪 Gaining Weight Fast
Baby gains about half a pound per week. Lungs nearly mature. Immune system strengthens. Baby is running out of room—movements feel different.
Weeks 37-40
🎉 Full Term & Ready!
Baby is considered full term at week 37. Lungs fully mature. Baby typically weighs 6-9 pounds. Head usually engages in pelvis. Any day now—your baby is ready to meet you!

🎯 Understanding the Three Trimesters

Each trimester brings unique changes to both mother and baby. Knowing what to expect helps you prepare physically, emotionally, and practically for each phase of pregnancy.

🌸 First Trimester

Weeks 1-12
  • ✓ Fertilization and implantation occur
  • ✓ All major organs begin forming
  • ✓ Heart starts beating (week 6)
  • ✓ Morning sickness common
  • ✓ Fatigue and breast tenderness
  • ✓ Frequent urination begins
  • ✓ Emotional changes and mood swings
  • ✓ First prenatal appointments
  • ✓ Genetic screening available
  • ✓ Critical period—avoid harmful substances

🌻 Second Trimester

Weeks 13-26
  • ✓ "Honeymoon phase"—energy returns
  • ✓ Baby bump becomes visible
  • ✓ Feel first movements (16-25 weeks)
  • ✓ Morning sickness usually subsides
  • ✓ Anatomy scan at week 20
  • ✓ Gender can be determined
  • ✓ Baby can hear sounds
  • ✓ Skin glow and hair changes
  • ✓ Round ligament pain possible
  • ✓ Start planning nursery

🍂 Third Trimester

Weeks 27-40
  • ✓ Final growth spurt for baby
  • ✓ Braxton Hicks contractions
  • ✓ Shortness of breath common
  • ✓ Frequent urination returns
  • ✓ Trouble sleeping
  • ✓ Swelling in feet and ankles
  • ✓ Baby drops into pelvis
  • ✓ Nesting instinct kicks in
  • ✓ Prepare hospital bag
  • ✓ Full term at week 37

📊 Due Date Accuracy & Statistics

While due dates provide a target, babies rarely arrive exactly on schedule. Understanding the statistics helps set realistic expectations and reduces anxiety as your due date approaches.

📈

Only 5% Deliver on Due Date

Just 1 in 20 babies arrive on their estimated due date. Most births occur within a two-week window around the due date.

📅

80% Deliver Within 2 Weeks

The vast majority of babies arrive between 38 and 42 weeks. This 4-week window is considered normal.

🔬

Ultrasound Dating Most Accurate

First-trimester ultrasounds can predict due dates within 5-7 days. Second-trimester scans are accurate within 10-14 days.

⏰

First Babies Often Late

First-time mothers typically deliver 3-5 days past their due date. Subsequent pregnancies often arrive closer to or before the due date.

👶

Average Pregnancy: 39 Weeks

While we calculate 40 weeks, research shows the average pregnancy lasts about 39 weeks and 5 days from LMP.

🌡️

Cycle Length Matters

Women with longer cycles often have later due dates than LMP calculations suggest, which is why we include cycle length adjustment.

⚖️ Comparing Due Date Calculation Methods

Different calculation methods suit different situations. Understanding when to use each method helps you get the most accurate estimate for your pregnancy.

🩸 Last Menstrual Period

Most Common
  • ✓ Standard method used by doctors
  • ✓ Easy to remember the date
  • ✓ Based on Naegele's Rule
  • ✓ Works best with regular cycles
  • ✗ Less accurate for irregular cycles
  • ✗ Assumes ovulation on day 14
  • Accuracy: ± 2 weeks
  • Best for: Women with regular 28-day cycles who remember their LMP

🥚 Conception Date

Most Accurate
  • ✓ Most accurate if date is known
  • ✓ Ideal for ovulation trackers
  • ✓ Bypasses cycle irregularities
  • ✓ Perfect for those trying to conceive
  • ✗ Requires knowing exact conception
  • ✗ Not always possible to pinpoint
  • Accuracy: ± 1 week
  • Best for: Women who tracked ovulation or had limited intercourse during fertile window

🔬 IVF Transfer Date

Precise
  • ✓ Exact embryo age known
  • ✓ No guessing about ovulation
  • ✓ Accounts for embryo development
  • ✓ Fertility clinic confirms timing
  • ✗ Only applicable to IVF pregnancies
  • ✗ Requires knowing transfer day (3 or 5)
  • Accuracy: ± 5 days
  • Best for: IVF, ICSI, and frozen embryo transfer pregnancies
💡 Pro Tip: Regardless of which method you use, your healthcare provider will likely confirm or adjust your due date with an early ultrasound. First-trimester ultrasound measurements of your baby's crown-rump length provide the most reliable dating and may supersede LMP-based calculations.

💡 Important Pregnancy Planning Tips

Now that you know your estimated due date, here are essential tips to help you prepare for your baby's arrival and maintain a healthy pregnancy.

🏥

Schedule Prenatal Care Early

Book your first prenatal appointment as soon as you know you're pregnant, ideally between weeks 8-10. Regular checkups monitor both your health and your baby's development.

💊

Start Prenatal Vitamins

Begin taking prenatal vitamins with folic acid immediately if you haven't already. Folic acid helps prevent neural tube defects and is crucial in early pregnancy.

🥗

Maintain Healthy Nutrition

Focus on a balanced diet rich in proteins, whole grains, fruits, vegetables, and healthy fats. Avoid raw fish, unpasteurized dairy, and limit caffeine to 200mg daily.

🏃‍♀️

Stay Active Safely

Moderate exercise like walking, swimming, and prenatal yoga benefits both you and baby. Always consult your provider before starting or continuing exercise routines.

😴

Prioritize Rest & Sleep

Growing a baby is hard work! Aim for 7-9 hours of sleep nightly. Sleep on your left side in later pregnancy to improve blood flow to your baby.

📝

Plan Ahead

Use your due date to plan maternity leave, prepare the nursery, attend childbirth classes, and arrange childcare. Start these tasks in the second trimester when energy levels are highest.

❓ Frequently Asked Questions

How accurate is a pregnancy due date calculator?
Pregnancy due date calculators provide estimates based on standardized formulas. The LMP method is accurate within about 2 weeks, while conception date calculations are accurate within about 1 week. However, only about 5% of babies are born on their exact due date. Most babies arrive within a 4-week window (38-42 weeks), which is considered normal. First-trimester ultrasounds provide the most accurate dating, typically within 5-7 days of the actual delivery date.
Why is pregnancy counted from the last menstrual period instead of conception?
Pregnancy is counted from the last menstrual period (LMP) because most women can reliably remember when their period started, while the exact moment of conception is often impossible to know. This dating convention was established long before modern fertility tracking methods existed. Technically, you're not actually pregnant during the first two weeks of your "pregnancy" using this method—conception typically occurs around day 14 of a 28-day cycle. This is why pregnancy is said to last 40 weeks from LMP but only 38 weeks from conception.
What if my cycle is longer or shorter than 28 days?
Our calculator adjusts for different cycle lengths. If your cycle is longer than 28 days, you likely ovulated later, meaning your due date would be later. If your cycle is shorter, you likely ovulated earlier, moving your due date earlier. For example, with a 35-day cycle, add 7 days to the standard calculation. With a 21-day cycle, subtract 7 days. This adjustment accounts for the variation in when you actually conceived relative to your LMP.
What's the difference between gestational age and fetal age?
Gestational age counts from your last menstrual period (LMP) and is used for pregnancy tracking and due date calculations. Fetal age (also called embryonic age or conceptional age) counts from the actual moment of conception and is approximately 2 weeks less than gestational age. When your doctor says you're "12 weeks pregnant," they mean 12 weeks gestational age, but your baby is actually only about 10 weeks old from conception. Medical professionals use gestational age because it's easier to calculate and standardize.
Can my due date change during pregnancy?
Yes, your due date may be adjusted, especially after your first ultrasound. If the ultrasound measurements differ significantly from your LMP-based due date (usually more than 5-7 days in the first trimester), your provider may change your official due date. This is common for women with irregular cycles or uncertain LMP dates. Once a due date is established by first-trimester ultrasound, it typically isn't changed again, as later ultrasounds are less accurate for dating.
What is considered full term pregnancy?
The American College of Obstetricians and Gynecologists (ACOG) defines pregnancy terms as follows: Early Term is 37 weeks 0 days through 38 weeks 6 days. Full Term is 39 weeks 0 days through 40 weeks 6 days. Late Term is 41 weeks 0 days through 41 weeks 6 days. Post-term is 42 weeks 0 days and beyond. Babies born at full term (39-40 weeks) typically have the best outcomes, which is why elective deliveries before 39 weeks are generally discouraged without medical necessity.
How is the due date calculated for IVF pregnancies?
IVF due dates are calculated from the embryo transfer date, which is precisely documented. For Day 3 embryo transfers, add 263 days (or subtract 3 days from transfer, then add 266 days). For Day 5 blastocyst transfers, add 261 days (or subtract 5 days from transfer, then add 266 days). Some fertility clinics calculate the "LMP equivalent" date for consistency with standard pregnancy dating. IVF dating is among the most accurate because the exact age of the embryo is known.
What are the signs that labor is approaching?
Common signs that labor may be near include: "Lightening" or the baby dropping lower into your pelvis, increased Braxton Hicks contractions, loss of the mucus plug (which may be bloody or "bloody show"), water breaking (rupture of membranes), regular contractions that increase in frequency and intensity, lower back pain, and nesting instinct. However, these signs can occur days or even weeks before actual labor begins. True labor is characterized by regular contractions that get closer together, longer, and stronger over time.
What happens if I go past my due date?
Going past your due date is very common—about 50% of pregnancies continue beyond 40 weeks. Your healthcare provider will monitor you more closely with non-stress tests and ultrasounds to check amniotic fluid levels and baby's movements. Most providers recommend induction between 41-42 weeks because risks (like decreased amniotic fluid and placental aging) increase after this point. However, some babies simply need a little more time. Your provider will discuss the best plan based on your individual circumstances.
Does the baby's gender affect the due date?
Research suggests slight differences, but they're not significant enough to change due date calculations. Some studies indicate that male babies tend to be born slightly later and female babies slightly earlier on average, but the difference is only about 1-2 days—well within the normal variation. Other factors like genetics, maternal age, and previous pregnancy history have a much larger impact on timing than the baby's gender.
How can I remember important pregnancy milestones?
Our calculator provides key milestone dates, but here are general guidelines to remember: First prenatal visit is typically weeks 8-10, first ultrasound is weeks 8-12, first trimester screening is weeks 11-13, gender can often be determined at weeks 18-20, anatomy scan is around week 20, viability milestone is week 24, glucose screening is weeks 24-28, Group B strep test is weeks 36-37, and full term begins at week 37. Download our results or add these dates to your calendar to stay on track.
Is there anything I can do to encourage labor naturally?
Once you reach full term (39+ weeks) and your provider confirms it's safe, some natural methods may help encourage labor, though scientific evidence varies. These include walking, gentle exercise, nipple stimulation, eating dates, and intimacy (semen contains prostaglandins). However, never attempt to induce labor before 39 weeks or without your provider's approval. Many "natural induction" methods have little scientific backing and some can be dangerous. The safest approach is patience—your baby will come when ready.

🌟 Track Your Pregnancy Journey

Congratulations on your pregnancy! Knowing your estimated due date is just the beginning of this incredible journey. Bookmark this calculator to check your progress weekly, share your due date with family and friends, and return to track important milestones. We wish you a healthy, happy pregnancy and a safe delivery!

📱

Save Your Results

Use the Copy or Print buttons to save your due date and key milestones for easy reference throughout your pregnancy.

📤

Share the News

Share your due date with family and friends using the Share button. Let loved ones know when to expect the newest family member!

🔄

Check Back Weekly

Return each week to see your updated progress, current week and trimester, baby's size comparison, and countdown to delivery.

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