Due Date Calculator - Calculate Your Baby’s Expected Arrival Date

Our free due date calculator helps you estimate when your baby will arrive based on your last menstrual period, conception date, or ultrasound results. Get a complete pregnancy timeline with trimester breakdown, important milestones, and key appointment dates.

What is a Due Date Calculator?

A due date calculator estimates your Expected Date of Delivery (EDD) - the day your baby is most likely to be born. Healthcare providers use this date to schedule prenatal appointments, monitor fetal development, and plan for delivery. The calculation is based on the standard 40-week (280-day) pregnancy duration from your last menstrual period.

Why Due Dates Matter

Your due date is essential for:

• Scheduling prenatal care: Timing ultrasounds, tests, and check-ups
• Monitoring fetal development: Ensuring baby grows at expected rate
• Planning maternity leave: Knowing when to prepare for baby’s arrival
• Medical decision-making: Determining if labor should be induced
• Preparing mentally and physically: Setting expectations for delivery timing

How Due Dates Are Calculated

Naegele’s Rule (LMP Method)

The most common method, Naegele’s Rule, calculates due date from your last menstrual period:

Formula:

1. Take the first day of your last menstrual period (LMP)
2. Add 1 year
3. Subtract 3 months
4. Add 7 days

Example:

• LMP: January 10, 2026
• Add 1 year: January 10, 2026
• Subtract 3 months: October 10, 2026
• Add 7 days: October 17, 2026 (Due Date)

Simplified: LMP + 280 days = Due Date

This method assumes:

• 28-day menstrual cycles
• Ovulation on day 14
• Fertilization within 24 hours of ovulation

Conception Date Method

If you know your conception date (from fertility treatment or tracking):

Formula: Conception Date + 266 days = Due Date

Why 266 days?

• Average pregnancy from conception: 38 weeks (266 days)
• This is 2 weeks less than the 40-week LMP calculation
• Accounts for the fact that conception occurs ~2 weeks after LMP

Example:

• Conception date: January 24, 2026
• Due date: October 17, 2026 (266 days later)

Ultrasound Dating Method

Most Accurate Method:

• First-trimester ultrasound (6-13 weeks)
• Measures crown-rump length (CRL)
• Accurate within ±5-7 days
• Becomes the official due date if it differs from LMP by >7 days

Why Ultrasound Dating is Superior:

• Accounts for irregular menstrual cycles
• Direct measurement of embryo/fetus
• Standardized growth patterns in early pregnancy
• Eliminates ovulation timing uncertainty

Due Date Accuracy: What to Expect

Statistical Reality

Important Facts:

• Only 5% of babies are born on their exact due date
• 80% are born within 2 weeks (before or after) due date
• 95% are born within 3 weeks of due date
• Due dates are estimates, not predictions

When Babies Typically Arrive

Timing	Percentage	Weeks
Before 37 weeks	10%	Preterm
37-38 weeks	30%	Early term
39-40 weeks	40%	Full term (optimal)
41 weeks	15%	Late term
42+ weeks	5%	Post term

First Baby vs. Subsequent Babies

First-Time Mothers:

• Average delivery: 40 weeks, 5 days
• More likely to deliver after due date
• Labor often longer

Experienced Mothers:

• Average delivery: 40 weeks, 1-2 days
• More likely to deliver before due date
• Labor often shorter

Average Difference: 3-5 days earlier for subsequent pregnancies

Pregnancy Timeline by Due Date

Trimester Breakdown

Once you know your due date, you can calculate your trimesters:

First Trimester (Weeks 1-13):

• Starts: First day of last period
• Ends: 13 weeks, 6 days
• Duration: 91-92 days
• Key developments: Organ formation, heartbeat begins

Second Trimester (Weeks 14-27):

• Starts: 14 weeks
• Ends: 27 weeks, 6 days
• Duration: 98 days
• Key developments: Movement felt, gender visible, rapid growth

Third Trimester (Weeks 28-40+):

• Starts: 28 weeks
• Ends: Birth
• Duration: 84-98+ days
• Key developments: Weight gain, lung maturation, positioning for birth

Important Milestone Dates

Based on your due date, you can calculate:

Milestone	Timing	What Happens
Implantation	3-4 weeks	Embryo attaches to uterus
Heartbeat Detectable	6 weeks	Visible on transvaginal ultrasound
Morning Sickness Peak	9-10 weeks	Nausea typically most severe
First Trimester End	13 weeks	Miscarriage risk drops significantly
Gender Often Visible	18-20 weeks	Anatomy scan
Viability	24 weeks	Baby could survive outside womb with medical care
Third Trimester	28 weeks	Final phase, rapid weight gain
Full Term	37 weeks	Baby considered full term
Optimal Delivery	39-40 weeks	Best outcomes for mother and baby
Post Dates	41+ weeks	Increased monitoring, induction considered

Prenatal Appointment Schedule

Standard Visit Timeline

First Trimester (Weeks 1-13):

• 6-8 weeks: First prenatal visit, pregnancy confirmation
• 8-14 weeks: First ultrasound (dating and viability)
• 10-13 weeks: NIPT genetic screening (optional)
• 11-14 weeks: Nuchal translucency scan (optional)

Second Trimester (Weeks 14-27):

• 15-20 weeks: Quad screen blood test (birth defect screening)
• 18-22 weeks: Anatomy scan (detailed ultrasound)
• 24-28 weeks: Glucose tolerance test (gestational diabetes)
• Monthly visits (every 4 weeks)

Third Trimester (Weeks 28-40+):

• 28 weeks: Rhogam shot (if Rh-negative)
• 28-36 weeks: Visits every 2 weeks
• 35-37 weeks: Group B Strep test
• 36+ weeks: Weekly visits until delivery

Key Tests by Week

Week	Test	Purpose
8-14	Dating ultrasound	Confirm due date, detect multiples
10-13	NIPT	Non-invasive genetic screening
15-20	Quad screen	Screen for Down syndrome, neural tube defects
18-22	Anatomy scan	Check fetal development, organs, gender
24-28	Glucose test	Screen for gestational diabetes
35-37	GBS test	Test for Group B Streptococcus

Factors That Affect Due Date Accuracy

Menstrual Cycle Regularity

Regular 28-Day Cycles:

• LMP method highly accurate
• Ovulation predictable (day 14)
• Due date calculation straightforward

Irregular Cycles:

• LMP method less reliable
• Ovulation timing varies
• Early ultrasound essential for accurate dating
• Conception date (if known) more accurate

Cycle Length Variations:

• Shorter cycles (21-24 days): May deliver slightly earlier
• Longer cycles (32-35 days): May deliver slightly later
• Adjustment: Add or subtract days based on typical cycle length

Multiple Pregnancies

Twins:

• Average delivery: 35-37 weeks
• Full term defined as 38 weeks (not 40)
• 50-60% deliver before 37 weeks

Triplets:

• Average delivery: 32-34 weeks
• High-risk for preterm delivery
• Specialized monitoring required

Higher Multiples:

• Typically deliver even earlier
• NICU care often needed

IVF and Assisted Reproduction

In Vitro Fertilization (IVF):

• Exact conception date known
• Due date = Transfer date + 266 days (for 3-day embryo)
• Due date = Transfer date + 264 days (for 5-day blastocyst)
• More accurate than LMP method

IUI (Intrauterine Insemination):

• Ovulation date known
• Due date = Insemination date + 266 days
• Assumes fertilization within 24 hours

What Changes Your Due Date?

Early Ultrasound Measurements

When Due Date Changes:

• First ultrasound shows >7 day difference from LMP date
• Healthcare provider will adjust to ultrasound date
• Becomes official due date for rest of pregnancy

Example:

• LMP-based due date: October 15
• 8-week ultrasound measures 9 weeks, 3 days
• New due date: October 5 (10 days earlier)
• New date used for all future planning

When Due Dates Don’t Change

Later Ultrasounds:

• Second/third trimester ultrasounds not used for dating
• Fetal growth varies too much individually
• Used only to monitor growth and development
• Original due date remains unchanged

Why Later Ultrasounds Aren’t Accurate for Dating:

• Genetic factors cause size variations
• Maternal nutrition affects growth
• Measurement errors increase with fetal size
• Accuracy decreases to ±2-3 weeks

Understanding Term Classifications

Full Term vs. Preterm vs. Post Term

Preterm (Before 37 Weeks):

• Extremely preterm: <28 weeks
• Very preterm: 28-32 weeks
• Moderate preterm: 32-34 weeks
• Late preterm: 34-37 weeks

Term Pregnancies:

• Early term: 37-38 weeks, 6 days
• Full term: 39-40 weeks, 6 days (optimal)
• Late term: 41-41 weeks, 6 days
• Post term: 42+ weeks

Why 39-40 Weeks is Optimal:

• Brain development peaks
• Lungs fully mature
• Best temperature regulation
• Lower NICU admission rates
• Better feeding outcomes
• Reduced respiratory issues

When Induction is Considered

Medical Reasons:

• Post-dates (41-42+ weeks)
• Gestational diabetes complications
• Preeclampsia or high blood pressure
• Decreased amniotic fluid
• Fetal growth concerns
• Placental problems

Elective Induction:

• Not recommended before 39 weeks
• Increased risks of C-section
• Best discussed with healthcare provider

Preparing for Your Due Date

Timeline for Preparation

By 20 Weeks:

• Choose healthcare provider and hospital
• Start prenatal vitamins
• Begin pregnancy education classes
• Plan budget for baby expenses

By 30 Weeks:

• Set up baby registry
• Start preparing nursery
• Purchase major items (crib, car seat, stroller)
• Attend childbirth education classes

By 36 Weeks:

• Pack hospital bag
• Install car seat
• Finalize birth plan
• Stock freezer with meals
• Arrange childcare for siblings

By 38 Weeks:

• Finish nursery setup
• Pre-register at hospital
• Know when to go to hospital (contraction timing)
• Have backup transportation plan

Hospital Bag Checklist

For Mom:

• ID, insurance cards, pre-registration papers
• Comfortable labor clothes
• Toiletries and personal items
• Going-home outfit
• Nursing bras and pads
• Phone charger

For Baby:

• Going-home outfit (2 sizes)
• Blanket
• Diapers (hospital usually provides)
• Car seat (must have to leave hospital)

For Partner:

• Snacks and drinks
• Phone charger
• Change of clothes
• Camera

Frequently Asked Questions

How accurate is a due date calculator?

Due date calculators provide estimates accurate within 1-2 weeks for women with regular cycles. Early ultrasound dating (before 13 weeks) is most accurate, within 5-7 days. Only about 5% of babies arrive on their exact due date.

Can I calculate my due date without knowing my last period?

Yes. An early ultrasound (ideally 8-13 weeks) can accurately determine your due date by measuring the embryo. This is actually more accurate than the LMP method, especially for women with irregular cycles.

What if my ultrasound due date is different from my LMP due date?

If the difference is more than 7 days, your healthcare provider will typically use the ultrasound date as your official due date. Early ultrasound measurements are more accurate than LMP calculations for most women.

Is my due date more accurate if I know my conception date?

Yes. If you know your exact conception date (from fertility tracking, IVF, or IUI), adding 266 days gives a very accurate due date. This method eliminates uncertainty about ovulation timing.

Will my baby be born on my due date?

Probably not. Only 5% of babies are born on their exact due date. However, 80% are born within 2 weeks (before or after) the due date, and 95% within 3 weeks.

Do first babies usually come late?

Yes, statistically first-time mothers deliver an average of 3-5 days later than experienced mothers. The average first baby arrives at 40 weeks, 5 days, while subsequent babies typically arrive around 40 weeks, 1-2 days.

What happens if I go past my due date?

If you reach 41 weeks without labor starting, your provider will likely increase monitoring (twice-weekly appointments, non-stress tests). Most providers recommend induction between 41-42 weeks to reduce risks to mother and baby.

Can my due date change during pregnancy?

Your due date can be adjusted based on an early ultrasound (before 13 weeks) if it differs significantly from your LMP-based date. After the first trimester, due dates rarely change. Later ultrasounds monitor growth but don’t change the due date.

How is due date calculated for twins?

Twins use the same calculation methods (LMP or conception date), but full term is considered 38 weeks instead of 40 weeks. Most twins deliver between 35-37 weeks naturally.

What’s the difference between due date and estimated delivery date?

They’re the same thing. “Due date” is the common term, while “Estimated Date of Delivery (EDD)” or “Estimated Date of Confinement (EDC)” are medical terms. All refer to the predicted day of birth.

Conclusion

Knowing your due date is one of the first exciting milestones of pregnancy. This free due date calculator provides science-based estimates using the same methods healthcare providers use worldwide.

While your due date gives you a target for planning and preparation, remember that it’s an estimate. Your baby will arrive when ready, typically somewhere within 3 weeks of your due date. Focus on healthy pregnancy habits, regular prenatal care, and preparing physically and emotionally for your new arrival.

Calculate your due date now to start planning for your baby’s arrival and tracking your pregnancy journey!

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Medical Disclaimer: This due date calculator is for informational purposes only and does not replace professional medical advice. Always consult with your obstetrician or healthcare provider for personalized pregnancy care. Your healthcare provider may adjust your due date based on ultrasound measurements and other clinical factors.