Pregnancy Due Date Calculator

Pregnancy Due Date Calculator - Calculate Baby Due Date

Calculate your pregnancy due date instantly with our free due date calculator. Based on your last menstrual period (LMP) or conception date, discover when to expect your baby and track your pregnancy progress through each trimester.

Calculate Your Due Date

Calculation Method:

• [Radio] Last Period (LMP)
• [Radio] Conception Date
• [Radio] IVF Transfer Date

Last Period / Conception Date:

• [Date Picker]

IVF Details (if applicable):

• [Dropdown] Day 3 Embryo / Day 5 Embryo

Cycle Length (Optional):

• [Input] days (default: 28 days)

[Calculate Due Date Button]

Your Results:

• Estimated Due Date: [Day of Week, Month DD, YYYY]
• Current Pregnancy Week: [Week X, Day Y]
• Current Trimester: [1st/2nd/3rd]
• Days Until Due Date: [XXX days]
• Conception Date: [Month DD, YYYY]
• Full-Term Range: [Month DD] - [Month DD]

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What is a Pregnancy Due Date?

The pregnancy due date (EDD - Expected Date of Delivery) is the estimated date when your baby is expected to be born. This date is calculated based on the first day of your last menstrual period (LMP) or, if known, the conception date.

Key Facts:

• Average pregnancy length: 280 days (40 weeks) from LMP
• Actual fetal development: 266 days (38 weeks) from conception
• Normal full-term range: 37-42 weeks
• Only 5% of babies are born on their exact due date
• Most births occur between 38-42 weeks

The due date is an estimate, not a deadline. Your healthcare provider will monitor your pregnancy and may adjust the due date based on ultrasound measurements and fetal development.

Why Calculate Your Due Date?

For Pregnancy Planning:

• Schedule prenatal care and appointments
• Plan maternity leave and work arrangements
• Prepare the nursery and baby essentials
• Arrange support and help for postpartum period

For Health Monitoring:

• Track fetal development milestones
• Monitor pregnancy progress week by week
• Understand which trimester you're in
• Know when to expect pregnancy symptoms

For Peace of Mind:

• Reduce anxiety about when baby will arrive
• Understand the normal range for delivery
• Prepare mentally and emotionally for birth
• Plan for the postpartum period

How Due Date is Calculated

Naegele's Rule

The Standard Calculation Method:

Naegele's Rule is the most common method for calculating pregnancy due dates:

Step 1: Find first day of last menstrual period (LMP)
Step 2: Add 1 year
Step 3: Subtract 3 months
Step 4: Add 7 days

OR SIMPLY: Add 280 days (40 weeks) to LMP

Example Calculation:

First Day of LMP: January 1, 2026

Calculation:
January 1 + 280 days = October 8, 2026

OR using Naegele's Rule:
January 1, 2026
+ 1 year = January 1, 2027
- 3 months = October 1, 2026
+ 7 days = October 8, 2026

Estimated Due Date: October 8, 2026

Alternative Calculation Methods

From Conception Date:

Due Date = Conception Date + 266 days (38 weeks)

Example:
Conception: April 17, 2026
Due Date: January 18, 2027

From IVF Transfer Date:

Day 5 Embryo (Blastocyst):

Due Date = Transfer Date + 266 days

Day 3 Embryo:

Due Date = Transfer Date + 268 days

From Ultrasound (Most Accurate):

Early ultrasound (before 13 weeks) measures crown-rump length (CRL) and provides the most accurate due date estimation, often more accurate than LMP dating.

Understanding the Calculation

Why 280 Days from LMP?

Breakdown:

• LMP to ovulation: ~14 days (follicular phase)
• Conception to birth: 266 days (38 weeks fetal development)
• Total: 280 days (40 weeks)

Important: The 280-day calculation assumes:

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

If Your Cycle Differs:

Cycle Length	Ovulation Day	Adjustment
26 days	Day 12	Add -2 days to due date
28 days	Day 14	Standard calculation
30 days	Day 16	Add +2 days to due date
32 days	Day 18	Add +4 days to due date

Our calculator can adjust for different cycle lengths for more accurate due date estimation.

Understanding Pregnancy Timeline

Trimester Breakdown

First Trimester (Weeks 1-13):

Period	Week Range	Key Developments
Month 1	Weeks 1-4	Fertilization, implantation
Month 2	Weeks 5-8	Heartbeat begins, organ formation
Month 3	Weeks 9-13	Fetal movement, fingerprints form

First Trimester Milestones:

• Week 4: Implantation complete, hCG detectable
• Week 5: Heart tube forms and begins to pulse
• Week 6: Heartbeat visible on ultrasound
• Week 8: Fetal movement begins (not yet felt)
• Week 9: Fetal kidneys function, baby urinates
• Week 10: All vital organs formed
• Week 12: Fingernails develop, gender determined
• End of Week 13: First trimester complete

Second Trimester (Weeks 14-27):

Period	Week Range	Key Developments
Month 4	Weeks 14-17	Quickening begins
Month 5	Weeks 18-22	Gender scan possible
Month 6	Weeks 23-27	Viability, lungs developing

Second Trimester Milestones:

• Week 14: Baby can squint, frown
• Week 15: Baby can sense light
• Week 16: Quickening (first movements felt by mom)
• Week 18: Gender determination possible via ultrasound
• Week 20: Halfway point, anatomy scan performed
• Week 21: Baby has eyebrows
• Week 24: Viable outside womb with medical care
• Week 27: Eyelids open, lungs developing
• End of Week 27: Second trimester complete

Third Trimester (Weeks 28-40+):

Period	Week Range	Key Developments
Month 7	Weeks 28-31	Rapid brain development
Month 8	Weeks 32-35	Weight gain, position changes
Month 9	Weeks 36-40+	Final preparation for birth

Third Trimester Milestones:

• Week 28: Baby responds to sounds and light
• Week 29: Baby can taste and smell
• Week 30: Baby produces surfactant (lung development)
• Week 31: Rapid weight gain begins
• Week 32: Baby practices breathing
• Week 34: Vernix coating thickens
• Week 36: Head may engage in pelvis
• Week 37: Full-term pregnancy begins
• Week 39: Full development complete
• Week 40: Estimated due date
• Week 42: Post-term pregnancy

Fetal Development by Week

Weeks 1-4 (First Month):

• Fertilization occurs
• Blastocyst implants in uterus
• Placenta begins to form
• Amniotic sac develops
• Embryo size: Poppy seed

Weeks 5-8 (Second Month):

• Heartbeat begins
• Major organs start forming
• Arms and legs buds appear
• Neural tube closes
• Facial features forming
• Fetus size: Raspberry (week 8)

Weeks 9-12 (Third Month):

• All organs present
• Fingers and toes formed
• Baby can make a fist
• Tooth buds appear
• Reproductive organs form
• Fetus size: Lime (week 12)

Weeks 13-16 (Fourth Month):

• Baby can suck thumb
• Skin is transparent
• Fine hair (lanugo) appears
• Baby can squint and frown
• Fetus size: Avocado (week 16)

Weeks 17-20 (Fifth Month):

• Quickening (mom feels movement)
• Baby hears sounds
• Skin covered in vernix
• Gender determination possible
• Fetus size: Banana (week 20)

Weeks 21-24 (Sixth Month):

• Baby has sleep cycles
• Lungs producing surfactant
• Eyebrows and eyelids present
• Taste buds developing
• Fetus size: Corn (week 24)

Weeks 25-28 (Seventh Month):

• Baby responds to light
• Eyes can blink
• Baby can dream (REM sleep)
• Gaining weight rapidly
• Fetus size: Eggplant (week 28)

Weeks 29-32 (Eighth Month):

• Baby practices breathing
• Stronger kicks and movements
• Bones hardening
• Positioning for birth
• Fetus size: Squash (week 32)

Weeks 33-36 (Ninth Month):

• Baby gaining 1oz per day
• Head may engage
• Vernix thickens
• Lung maturation complete
• Fetus size: Honeydew (week 36)

Weeks 37-40 (Tenth Month):

• Full-term baby
• Ready for birth
• Average weight: 6-9 lbs
• Average length: 19-21 inches
• Fetus size: Watermelon (week 40)

Due Date Accuracy

Understanding Due Date Variations

Birth Statistics:

• 5% of babies born on exact due date
• 25% born within 3 days of due date
• 50% born within 1 week of due date
• 75% born within 2 weeks of due date
• 90% born within 3 weeks of due date

Normal Delivery Range:

Category	Week Range	Percentage of Births
Preterm	Before 37	~10%
Early Term	37-38	~25%
Full Term	39-40	~50%
Late Term	41	~10%
Post-Term	42+	~5%

Factors Affecting Due Date Accuracy

1. Irregular Menstrual Cycles:

• LMP dating assumes regular cycles
• Harder to pinpoint ovulation
• Ultrasound dating more accurate
• May need due date adjustment

2. Cycle Length Variations:

• Shorter cycles (<28 days): May be further along
• Longer cycles (>28 days): May be less far along
• Our calculator adjusts for this
• Ovulation timing affects accuracy

3. Ovulation Timing:

• Ovulation not always day 14
• Can vary cycle to cycle
• Stress affects ovulation
• Multiple possible conception dates

4. First Pregnancy vs. Subsequent:

• First babies: Often arrive later (average 41 weeks)
• Subsequent babies: May arrive earlier (average 39-40 weeks)
• Each pregnancy is different
• Previous birth history helps predict

5. Ultrasound Dating:

• Early ultrasound (before 13 weeks): Most accurate (±5 days)
• Mid-pregnancy (14-27 weeks): Moderate accuracy (±7-10 days)
• Late pregnancy (28+ weeks): Least accurate (±2-3 weeks)

When Due Dates Change

Common Reasons for Due Date Adjustment:

1. Early Ultrasound Discrepancy:

• Ultrasound more accurate than LMP
• Difference of >5-7 days triggers adjustment
• Earlier ultrasound takes precedence
• Most common reason for change

2. IVF Pregnancies:

• Known conception date
• Precise embryo age
• Due date based on transfer date
• More accurate from the start

3. Fundal Height Measurements:

• Uterus size measured during prenatal visits
• Measures baby's growth
• Can indicate dating discrepancies
• May prompt ultrasound reassessment

4. Multiple Pregnancy:

• Twins/triplets typically arrive early
• Average twin delivery: 35-37 weeks
• Due date may be adjusted for planning
• More frequent monitoring required

Pregnancy Milestones

Key Prenatal Appointments

First Trimester Visits:

Week 6-8: Initial Prenatal Visit:

• Confirm pregnancy
• Calculate due date
• Health history review
• Blood work and screenings
• Prescribe prenatal vitamins

Week 11-13: First Trimester Screening:

• Ultrasound for nuchal translucency
• Blood tests for chromosomal abnormalities
• Early anatomy check
• Due date confirmation

Second Trimester Visits:

Week 16: Monthly Checkup:

• Fundal height measurement
• Fetal heart rate check
• Mother's weight and blood pressure
• Discuss quickening (movement)

Week 20: Anatomy Scan:

• Detailed ultrasound examination
• Gender determination (if desired)
• Placenta location check
• Amniotic fluid assessment

Week 24-28: Glucose Screening:

• Gestational diabetes test
• Rh factor screening
• Anemia check
• Third trimester planning

Third Trimester Visits:

Week 28: Begin Bi-Weekly Visits:

• Fetal growth monitoring
• Kick count instructions
• Signs of preterm labor
• Birth plan discussion

Week 32: Growth Check:

• Ultrasound if needed
• Baby position check
• Discuss cesarean if needed
• Preterm labor signs

Week 36: Weekly Visits Begin:

• Group B Strep test
• Cervical checks may begin
• Baby position monitoring
• Birth plan finalization

Week 38-40: Final Weeks:

• Weekly or twice-weekly visits
• Cervical ripeness assessment
• Non-stress tests if needed
• Discussion of induction if past due date

Important Pregnancy Milestones

Week 6: Heartbeat detectable on ultrasound Week 12: End of first trimester (miscarriage risk decreases) Week 16: Quickening (first movements felt) Week 20: Halfway point, gender scan possible Week 24: Age of viability (baby could survive outside womb) Week 27: End of second trimester Week 28: Third trimester begins Week 37: Full-term pregnancy begins Week 40: Estimated due date Week 42: Post-term pregnancy (consider induction)

Special Circumstances

Twins and Multiples

Multiple Pregnancy Timeline:

Type	Average Delivery	Due Date Consideration
Twins	35-37 weeks	Often 3-5 weeks early
Triplets	32-34 weeks	Often 6-8 weeks early
Quadruplets	28-30 weeks	Often 10+ weeks early

Multiple Pregnancy Considerations:

• More frequent prenatal visits
• Earlier and more frequent ultrasounds
• Higher risk of preterm labor
• Possible bed rest in third trimester
• Delivery planning more complex

Due Date Calculator for Multiples:

• Still use LMP or conception date
• Understand early delivery is likely
• Plan for earlier maternity leave
• Prepare for potential NICU time

IVF Pregnancy

IVF Due Date Calculation:

Fresh Embryo Transfer:

Due Date = Egg Retrieval Date + 266 days

OR

Day 3 Transfer: +268 days
Day 5 Transfer: +266 days

Frozen Embryo Transfer (FET):

Due Date = Transfer Date + 266 days (day 5)
OR Transfer Date + 268 days (day 3)

IVF Advantages:

• Most accurate due date possible
• Known conception date
• Early monitoring available
• Fewer dating discrepancies

Irregular Periods

Calculating Due Date with Irregular Cycles:

Challenges:

• LMP may be unreliable
• Ovulation date uncertain
• Conception timing unclear
• Ultrasound dating preferred

Solutions:

• Early ultrasound for accurate dating
• Use conception date if known
• Consider ovulation tracking data
• Healthcare provider will establish due date

How do I calculate my due date?

Calculate your due date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). Alternatively, add 266 days (38 weeks) to your conception date if known. Our pregnancy due date calculator performs this calculation instantly - just enter your LMP or conception date.

What is my due date based on my last period?

Your due date is approximately 280 days (40 weeks) from the first day of your last menstrual period. For example, if your LMP was January 1, your estimated due date would be October 8. Enter your LMP into our due date calculator for instant calculation.

How accurate are due date calculations?

Due dates are estimates - only 5% of babies are born on their exact due date. Most arrive within 2 weeks before or after (38-42 weeks). Early ultrasound (before 13 weeks) provides the most accurate dating and may adjust your due date by a few days to a week.

Can I calculate my due date from conception?

Yes, if you know your conception date, add 266 days (38 weeks) to estimate the due date. Conception typically occurs about 14 days after the start of your last period for a 28-day cycle. Our calculator can calculate from either LMP or conception date.

How many weeks pregnant am I?

Your pregnancy weeks are counted from the first day of your last menstrual period (LMP) to today's date. Our pregnancy calculator shows your current gestational age in weeks and days based on your LMP or due date. This is called "gestational age" and includes the 2 weeks before conception occurred.

What if my periods are irregular?

With irregular periods, LMP dating may be inaccurate. Rely on early ultrasound (before 13 weeks) for the most accurate due date estimation. Our calculator provides an estimate based on LMP, but your healthcare provider will confirm or adjust based on ultrasound measurements.

How is due date calculated with IVF?

For IVF pregnancies, calculate from the embryo transfer date. Add 266 days for day 5 embryos (blastocysts) or 268 days for day 3 embryos. For fresh transfers, you can also calculate from egg retrieval date. IVF due dates are typically more accurate than natural conception due to known dates.

What is considered full-term pregnancy?

Full-term pregnancy is 39-40 weeks. Early term is 37-38 weeks, late term is 41 weeks, and post-term is 42+ weeks. Babies born at 37 weeks or later are considered full-term and have fully developed organs ready for life outside the womb.

When is my due date based on conception date?

If you know your conception date, add 266 days (38 weeks) to find your due date. Conception typically occurs about 14 days after the start of your last period. For example, conception on April 17 gives a due date of approximately January 18 of the following year.

Why do doctors use LMP instead of conception date?

Most women know their LMP date but not their exact conception date. Ovulation and conception can vary from cycle to cycle, while LMP is a fixed date. However, early ultrasound is more accurate than LMP dating and may adjust the due date if there's a significant discrepancy.

Is this pregnancy due date calculator free?

Yes, our pregnancy due date calculator is completely free with unlimited calculations. No registration or payment required. Calculate your due date and track your pregnancy progress as often as needed.

Can due dates change during pregnancy?

Yes, due dates can change based on early ultrasound measurements. If early ultrasound shows a discrepancy of more than 5-7 days from the LMP-based due date, your healthcare provider will adjust your due date. Early ultrasound dating is considered more accurate than LMP.

What's the difference between gestational age and fetal age?

Gestational age counts from the first day of your last period (includes 2 weeks before conception). Fetal age (or embryonic age) counts from the actual conception date. Healthcare providers use gestational age, which is 2 weeks longer than fetal age. Our calculator shows gestational age.

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Practice Examples

Example 1: Regular 28-Day Cycle

Pregnancy Information:

• First Day of Last Period: March 1, 2026
• Regular 28-day cycle
• Ovulation on day 14 (March 15)

Calculation:

Due Date = LMP + 280 days
Due Date = March 1, 2026 + 280 days
Due Date = December 6, 2026

Conception Date = March 15, 2026 (approximately)
Current Pregnancy (if today is June 1): 13 weeks, 0 days
Trimester: Second trimester

Results:

• Due Date: December 6, 2026
• Conception: ~March 15, 2026
• Full-Term Range: November 15 - December 20, 2026
• Current Trimester: 2nd

Example 2: Known Conception Date

Pregnancy Information:

• Conception Date: May 10, 2026
• Conceived through fertility treatment
• Exact date known

Calculation:

Due Date = Conception Date + 266 days
Due Date = May 10, 2026 + 266 days
Due Date = January 31, 2027

Estimated LMP = April 26, 2026 (14 days before conception)

Results:

• Due Date: January 31, 2027
• LMP (estimated): April 26, 2026
• Full-Term Range: January 10 - February 14, 2027
• Current Trimester: Based on today's date

Example 3: IVF Pregnancy (Day 5 Transfer)

Pregnancy Information:

• IVF Day 5 Embryo Transfer: June 15, 2026
• Frozen embryo transfer
• Known embryo age

Calculation:

Due Date = Transfer Date + 266 days
Due Date = June 15, 2026 + 266 days
Due Date = March 8, 2027

Conception Date = June 10, 2026 (fertilization)
LMP (estimated) = May 27, 2026

Results:

• Due Date: March 8, 2027
• Conception: June 10, 2026
• Full-Term Range: February 15 - March 22, 2027
• Pregnancy Progress: Based on exact dates

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Related Tools

• Ovulation Calculator
• Conception Calculator
• Pregnancy Weight Gain Calculator
• BMI Calculator
• Fertility Calculator

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Need Help? Our pregnancy due date calculator is perfect for newly pregnant women, those planning pregnancy, or anyone tracking their pregnancy journey. Calculate your due date now and prepare for your baby's arrival!

Disclaimer: This pregnancy due date calculator provides estimates based on standard pregnancy calculations. Due dates are estimates only - only 5% of babies are born on their exact due date. Always consult with healthcare providers for accurate pregnancy dating, prenatal care, and medical advice.