Pregnancy Calculator

About Pregnancy Calculator

Our pregnancy calculator is a comprehensive tool designed to help expecting mothers calculate their due date, track pregnancy progress, and understand important milestones throughout their pregnancy journey. Whether you know your last menstrual period, conception date, due date, or have ultrasound information, our calculator provides accurate pregnancy timeline information.

How to Use the Pregnancy Calculator

We offer five different calculation methods to accommodate various situations:

1. Last Menstrual Period (LMP)

This is the most common method used by healthcare providers. Simply enter the first day of your last menstrual period and your average cycle length. The calculator uses Naegele's rule to estimate your due date by adding 280 days (40 weeks) to your LMP date, adjusted for your cycle length if different from 28 days.

• Most accurate if you have regular menstrual cycles
• Standard method used by doctors and midwives
• Can be adjusted for cycle lengths from 21 to 35 days
• Assumes ovulation occurs around day 14 of a 28-day cycle

2. Conception Date

If you know the exact date of conception (such as from fertility tracking or assisted reproduction), this method provides a highly accurate due date calculation. The calculator adds 266 days (38 weeks) from the conception date.

• Most accurate if you know the exact conception date
• Useful for those who track ovulation carefully
• Ideal for planned pregnancies with known intercourse dates
• Provides precise gestational age calculations

3. Due Date

If your healthcare provider has already given you a due date (perhaps from an early ultrasound), you can work backward to determine other pregnancy milestones and your current week of pregnancy.

• Useful when due date has been established by a doctor
• Calculates backwards to estimate LMP and conception
• Helps track remaining pregnancy timeline
• Good for second opinions on pregnancy progress

4. Ultrasound Date

Early ultrasounds (especially those done between 8-13 weeks) are very accurate for dating pregnancy. Enter the ultrasound date and the gestational age provided by your sonographer to get an adjusted due date.

• Most accurate method, especially for early ultrasounds
• Corrects for irregular cycles or uncertain LMP
• Uses actual fetal measurements for dating
• Standard for dating pregnancies in modern obstetrics

5. IVF Transfer Date

For pregnancies resulting from in vitro fertilization (IVF), the embryo transfer date and embryo age provide the most accurate pregnancy dating. Choose whether you had a day 3 or day 5 transfer.

• Most precise method for IVF pregnancies
• Accounts for embryo age at transfer
• Day 5 transfers (blastocyst stage) most common
• Eliminates uncertainty about conception timing

Understanding Your Results

After calculation, you'll receive comprehensive information about your pregnancy:

Due Date

Your estimated due date (EDD) is the day your baby is expected to arrive, calculated as 40 weeks from your LMP or 38 weeks from conception. Remember that only about 5% of babies arrive exactly on their due date. Most babies are born within two weeks before or after the due date, which is considered normal and "full term."

Current Pregnancy Week

Pregnancy is measured in weeks and days from your last menstrual period. For example, "15 weeks, 3 days" means you are in your 16th week of pregnancy. Healthcare providers use this system because it's standardized and easy to track, even though conception typically occurs about 2 weeks after the LMP.

Trimester Information

Pregnancy is divided into three trimesters:

• First Trimester (Weeks 1-13): Major organ development, morning sickness common, highest risk of miscarriage
• Second Trimester (Weeks 14-27): Baby grows rapidly, movements felt, often called the "honeymoon period"
• Third Trimester (Weeks 28-40+): Final growth and maturation, preparing for birth, increased discomfort

Progress Bar

The visual progress bar shows how far along you are in your pregnancy journey, displayed as both weeks and percentage completed. This helps you visualize your progress toward meeting your baby.

Important Pregnancy Milestones

Our calculator provides dates for significant pregnancy milestones:

Conception Date (Week 2)

The estimated date when fertilization occurred. While pregnancy is counted from your LMP, actual conception happens about 2 weeks later during ovulation. This is when sperm meets egg and pregnancy truly begins.

Heartbeat Detection (Week 6)

Around 6 weeks from LMP (4 weeks from conception), your baby's heart begins beating. This can often be detected via ultrasound, though sometimes it takes until 7-8 weeks. The heart starts at about 90-110 beats per minute and increases to 140-170 bpm by 9 weeks.

End of First Trimester (Week 13)

This marks the completion of the first trimester. By this point, all major organs have formed, the risk of miscarriage drops significantly, and many women start feeling better as morning sickness subsides. The baby is now called a fetus and is about 3 inches long.

First Movements/Quickening (Weeks 18-20)

First-time mothers typically feel baby's movements between weeks 18-20, while women who have been pregnant before may notice them as early as week 16. Initially, movements feel like flutters, bubbles, or light tapping.

Viability (Week 24)

The age of viability is generally considered to be around 24 weeks, when a baby has a chance of survival outside the womb with intensive medical care. Survival rates and outcomes improve significantly with each additional week of development.

End of Second Trimester (Week 27)

This marks entry into the third and final trimester. The baby's lungs, though immature, are developing the ability to breathe air. Most babies born at this stage have an excellent chance of survival with medical support.

Full Term (Week 37)

Pregnancies are considered "full term" at 37 weeks. Babies born at this stage are generally healthy and require minimal medical intervention. However, babies benefit from staying in the womb until at least 39 weeks when possible.

Due Date (Week 40)

Your estimated due date at 40 weeks. While this is the target date, it's completely normal to go into labor anywhere from 37 to 42 weeks. Only about 5% of babies arrive on their exact due date.

Understanding Pregnancy Dating

It may seem confusing that pregnancy is 40 weeks long but gestation is only 38 weeks. Here's why:

• Gestational Age: Calculated from the first day of your last menstrual period (40 weeks)
• Fetal Age: Calculated from conception, about 2 weeks later (38 weeks)
• Doctors use gestational age because it's easier to track and standardized
• You're actually not pregnant during the first 2 weeks of "pregnancy"

How Accurate Are Due Date Calculations?

Due date accuracy depends on the calculation method:

• Ultrasound (8-13 weeks): Most accurate, within 3-5 days
• IVF Transfer Date: Extremely accurate, within 1-2 days
• Known Conception Date: Very accurate, within 3-5 days
• Regular LMP: Accurate within 7-10 days
• Irregular Cycles: Less accurate, may need ultrasound adjustment

When Due Dates Change

Your due date may be adjusted if:

• An early ultrasound shows different dating by more than 5-7 days
• You have irregular menstrual cycles
• You're uncertain about your LMP date
• You were on hormonal birth control when you conceived
• You're breastfeeding and cycles haven't normalized

Cycle Length and Due Date

Most due date calculations assume a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, this affects your due date:

• Shorter cycles (21-27 days): Ovulation occurs earlier, due date may be earlier
• Longer cycles (29-35 days): Ovulation occurs later, due date may be later
• Our calculator adjusts for cycle lengths from 21-35 days
• If cycles are irregular, ultrasound dating is more reliable

Pregnancy Weeks vs. Months

Pregnancy is 40 weeks, which equals approximately 9 months and 1 week (not 9 months exactly). Here's the breakdown:

• Month 1: Weeks 1-4
• Month 2: Weeks 5-8
• Month 3: Weeks 9-13
• Month 4: Weeks 14-17
• Month 5: Weeks 18-22
• Month 6: Weeks 23-27
• Month 7: Weeks 28-31
• Month 8: Weeks 32-35
• Month 9: Weeks 36-40

What is Naegele's Rule?

Naegele's rule is the standard method for calculating due dates, developed in the 1800s by German obstetrician Franz Naegele. The formula is:

• Take the first day of your last menstrual period
• Add 1 year
• Subtract 3 months
• Add 7 days

For example: LMP of January 1, 2024 → Due date of October 8, 2024

When Will Labor Start?

While we can calculate a due date, predicting the exact day of labor is impossible. Statistics show:

• Only 5% of babies arrive on their due date
• First babies tend to arrive after their due date
• Subsequent pregnancies may deliver earlier
• Most babies arrive between 37-42 weeks
• Induction may be recommended after 41-42 weeks

Full Term Definitions

The American College of Obstetricians and Gynecologists (ACOG) defines term pregnancy as:

• Early Term: 37 weeks 0 days to 38 weeks 6 days
• Full Term: 39 weeks 0 days to 40 weeks 6 days
• Late Term: 41 weeks 0 days to 41 weeks 6 days
• Post Term: 42 weeks 0 days and beyond

Premature Birth

Babies born before 37 weeks are considered premature:

• Late Preterm: 34-36 weeks (usually good outcomes)
• Moderately Preterm: 32-34 weeks (may need NICU care)
• Very Preterm: 28-32 weeks (requires intensive care)
• Extremely Preterm: Less than 28 weeks (highest risk)

Signs of Labor

Watch for these signs as your due date approaches:

• Regular contractions that increase in frequency and intensity
• Water breaking (rupture of membranes)
• Bloody show (mucus plug discharge)
• Lower back pain that comes in waves
• Strong urge to nest or sudden energy burst

Factors Affecting Pregnancy Length

Several factors can influence when you go into labor:

• First vs. subsequent pregnancies: First babies often arrive later
• Mother's age: Older mothers may have longer pregnancies
• Baby's size: Larger babies may come earlier
• Genetics: Family history of early or late births
• Multiple pregnancy: Twins typically arrive 3-4 weeks early
• Health conditions: Certain conditions may affect timing

IVF and Pregnancy Dating

IVF pregnancies are dated differently than natural pregnancies:

• Day 3 Transfer: Transfer date is considered 17 days past LMP
• Day 5 Transfer: Transfer date is considered 19 days past LMP
• This accounts for the embryo's age at transfer
• IVF dating is extremely accurate since conception timing is known
• Due date calculation: Transfer date + 266 days - embryo age

Ultrasound Dating

Ultrasounds date pregnancy by measuring the baby:

• 6-7 weeks: Crown-rump length (CRL) measurement
• 8-13 weeks: Most accurate window for dating (±3-5 days)
• Second trimester: Multiple measurements used (±1-2 weeks)
• Third trimester: Less accurate for dating (±2-3 weeks)
• Earlier ultrasounds are more accurate for dating

Multiple Pregnancies

Twin and multiple pregnancies have different timelines:

• Twins: Average delivery at 36-37 weeks
• Triplets: Average delivery at 32-33 weeks
• Multiple pregnancies rarely go to 40 weeks
• Dating methods are the same, but monitoring is increased
• Growth patterns differ from singleton pregnancies

Planning for Baby's Arrival

Use your due date to plan important preparations:

• 36 weeks: Hospital bag packed, birth plan finalized
• 34-36 weeks: Nursery ready, car seat installed
• 32-34 weeks: Childbirth classes completed
• Before 32 weeks: Major purchases made, baby shower held
• Plan for baby to arrive 2-3 weeks early or late

Important Prenatal Appointments

Standard prenatal care schedule:

• Weeks 4-28: Monthly visits
• Weeks 28-36: Every 2 weeks
• Weeks 36-40: Weekly visits
• After 40 weeks: Twice weekly monitoring
• High-risk pregnancies require more frequent visits

Common Prenatal Tests Timeline

• 6-8 weeks: First ultrasound, confirm pregnancy
• 10-13 weeks: First trimester screening, NT scan
• 15-20 weeks: Quad screen, amniocentesis (if needed)
• 18-22 weeks: Anatomy scan (detailed ultrasound)
• 24-28 weeks: Glucose screening for gestational diabetes
• 35-37 weeks: Group B strep screening

Limitations of Due Date Calculators

While our calculator is accurate, remember:

• Due dates are estimates, not guarantees
• Normal pregnancy length varies by 5 weeks (37-42 weeks)
• Individual factors affect actual delivery date
• Always consult healthcare providers for medical decisions
• Ultrasound dating may override LMP-based dates

When to Contact Your Healthcare Provider

Contact your provider immediately if you experience:

• Severe abdominal pain or cramping
• Heavy bleeding or passing tissue
• Sudden swelling of face, hands, or feet
• Severe headaches with vision changes
• Reduced fetal movement after 28 weeks
• Signs of preterm labor before 37 weeks
• Water breaking before 37 weeks

Healthy Pregnancy Tips

• Take prenatal vitamins with folic acid (400-800 mcg daily)
• Attend all prenatal appointments
• Eat a balanced diet with plenty of fruits, vegetables, and protein
• Stay hydrated (8-10 glasses of water daily)
• Get regular, moderate exercise (with provider approval)
• Get adequate sleep (7-9 hours nightly)
• Avoid alcohol, smoking, and recreational drugs
• Limit caffeine (less than 200mg daily)

Frequently Asked Questions

How accurate is this pregnancy calculator?

Our calculator uses the same methods as healthcare providers. LMP-based calculations are accurate within 7-10 days for women with regular cycles. Ultrasound-based calculations (especially between 8-13 weeks) are accurate within 3-5 days. IVF transfer dates provide the most accurate predictions.

Can my due date change?

Yes, due dates are often adjusted after an early ultrasound, especially if the ultrasound date differs from the LMP date by more than 5-7 days. First-trimester ultrasounds are considered the gold standard for dating pregnancy.

What if I don't know my LMP?

If you don't remember your last period, an early ultrasound (ideally between 8-13 weeks) can accurately date your pregnancy. You can also use the conception date calculator if you know approximately when conception occurred.

Is pregnancy really 9 months?

Pregnancy is 40 weeks, which is approximately 9 months and 1 week (280 days). Some months have 4 weeks while others have 4-5 weeks, which is why the "9 months" is approximate.

Why do they count from my last period if I wasn't pregnant then?

This is a standardized system that's easy to track since most women know when their last period started. Conception typically occurs about 2 weeks after your LMP during ovulation, but using LMP provides a consistent starting point.

When will I start showing?

First-time mothers typically start showing between 12-16 weeks. Women who have been pregnant before may show earlier (8-12 weeks). Body type, fitness level, and baby's position also affect when you show.

When can I find out the baby's sex?

The anatomy ultrasound at 18-22 weeks can usually determine sex, though it may be visible as early as 14-16 weeks. Blood tests (NIPT) can determine sex as early as 10 weeks.

What if my baby comes early or late?

Only 5% of babies arrive on their due date. Delivery anytime between 37-42 weeks is considered normal and healthy. Your healthcare provider will monitor you more closely after 40-41 weeks and may discuss induction options.

Disclaimer

This pregnancy calculator is for informational purposes only and should not replace professional medical advice. Always consult with your healthcare provider for personalized pregnancy care, accurate dating, and medical decisions. This calculator provides estimates based on standard formulas but individual pregnancies vary. Contact your healthcare provider immediately if you have any concerns about your pregnancy.

Privacy and Security

All calculations are performed directly in your browser using JavaScript. We do not store, collect, or transmit any of your personal pregnancy information. Your data remains completely private on your device.