Pregnancy Due Date Calculator
Calculate your pregnancy due date, current week, trimester, and baby size. Track milestones from conception to delivery.
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About This Calculator
The Pregnancy Due Date Calculator helps expectant parents estimate when their baby will arrive. Using the same method doctors use - Naegele's rule - this calculator determines your estimated due date (EDD) based on the first day of your last menstrual period (LMP) or your known conception date.
Understanding your due date is essential for tracking pregnancy progress, scheduling prenatal appointments, and preparing for your baby's arrival. While only about 5% of babies are born exactly on their due date, knowing your EDD helps you and your healthcare provider monitor fetal development and plan for important milestones throughout your pregnancy journey.
Our free pregnancy calculator provides instant results including your current week of pregnancy, trimester, days remaining, a visual progress bar, baby size comparisons (using fun fruit and vegetable analogies), and a complete timeline of key pregnancy milestones from first heartbeat to delivery day.
Disclaimer: This calculator is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider for personalized prenatal care and accurate dating of your pregnancy.
How to Use the Pregnancy Due Date Calculator
- 1**Choose your input method**: Select either "Last Menstrual Period" (most common) or "Conception Date" (if you know your exact conception date from IVF or ovulation tracking). The LMP method is what most doctors use.
- 2**Enter the first day of your last period**: If using the LMP method, enter the first day of your last menstrual period. This is NOT the end date of your period - it is the first day bleeding began. This date is typically 2 weeks before conception.
- 3**Adjust cycle length if needed**: The default is 28 days, which is average. If your cycles are regularly shorter (e.g., 26 days) or longer (e.g., 32 days), adjust this setting for a more accurate due date calculation. Cycle length affects when ovulation likely occurred.
- 4**Or enter conception date directly**: If you know your conception date (common with IVF, fertility treatments, or careful ovulation tracking), select the Conception Date tab and enter that date. Due date will be calculated as 266 days (38 weeks) from conception.
- 5**Review your results**: Your estimated due date, current week of pregnancy, trimester, and days remaining will be displayed immediately. The progress bar shows how far along you are in your 40-week pregnancy journey.
- 6**Explore milestones and baby size**: Scroll down to see what size your baby is compared to fruits and vegetables, key pregnancy milestones you have passed or are approaching, and important dates like trimester boundaries and full-term date.
Naegele's Rule: How Due Dates Are Calculated
Naegele's rule is the standard method used by healthcare providers worldwide to calculate pregnancy due dates. Named after German obstetrician Franz Karl Naegele (1778-1851), this simple formula has been the foundation of obstetric dating for over 200 years.
The Naegele's Rule Formula
From Last Menstrual Period (LMP):
Due Date = LMP + 280 days (40 weeks)
Alternative calculation:
Due Date = LMP + 1 year - 3 months + 7 days
From Conception Date:
Due Date = Conception Date + 266 days (38 weeks)
Step-by-Step Example
If your LMP was January 1, 2026:
- Add 280 days to January 1, 2026
- Due Date: October 8, 2026
Or using the alternative method:
- January 1, 2026 + 1 year = January 1, 2027
- January 1, 2027 - 3 months = October 1, 2026
- October 1, 2026 + 7 days = October 8, 2026
Why 280 Days?
The 280-day calculation (40 weeks) assumes:
- A 28-day menstrual cycle
- Ovulation occurring on day 14 of the cycle
- Pregnancy lasting 266 days (38 weeks) from conception
- The extra 14 days account for the time between LMP and ovulation
Cycle Length Adjustments
If your cycle differs from 28 days:
- Shorter cycles (e.g., 25 days): Subtract the difference from due date
- Longer cycles (e.g., 35 days): Add the difference to due date
For example, with a 35-day cycle, add 7 days to the standard calculation because ovulation likely occurred on day 21 instead of day 14.
Understanding Pregnancy Trimesters
Pregnancy is divided into three trimesters, each lasting approximately 13-14 weeks. Understanding these stages helps you track development and know what to expect at each phase.
First Trimester (Weeks 1-12)
Key Developments:
- Week 4: Implantation occurs; pregnancy test may become positive
- Week 5-6: Heart begins to beat (often visible on early ultrasound)
- Week 8: All major organs are forming; embryo becomes a fetus
- Week 10: Fingers and toes are fully formed
- Week 12: Baby is about 2 inches long; risk of miscarriage decreases significantly
Common Symptoms:
- Morning sickness and nausea
- Fatigue and increased need for sleep
- Breast tenderness and changes
- Frequent urination
- Food aversions or cravings
Important Appointments:
- First prenatal visit (usually weeks 8-10)
- Dating ultrasound to confirm due date
- First trimester screening (weeks 11-13)
Second Trimester (Weeks 13-27)
Key Developments:
- Week 16: Gender may be visible on ultrasound
- Week 18-22: Most women feel first movements ("quickening")
- Week 20: Anatomy scan to check baby's development
- Week 24: Viability milestone - baby has a chance of survival if born
- Week 27: Eyes can open; baby responds to light and sound
Common Experiences:
- Morning sickness typically improves
- Energy levels often increase
- Baby bump becomes visible
- Feeling baby's movements
- Possible round ligament pain
Important Appointments:
- Anatomy ultrasound (weeks 18-22)
- Glucose screening for gestational diabetes (weeks 24-28)
Third Trimester (Weeks 28-40+)
Key Developments:
- Week 28: Brain develops rapidly; baby practices breathing
- Week 32: Lungs continue maturing; baby gains weight quickly
- Week 36: Baby may "drop" into pelvis (engagement)
- Week 37: Baby is considered full term
- Week 40: Due date - baby is ready for birth
Common Experiences:
- Increased discomfort and fatigue
- Braxton Hicks contractions
- Shortness of breath
- Difficulty sleeping
- Nesting instinct
- Frequent urination returns
Important Appointments:
- Weekly or biweekly prenatal visits
- Group B strep test (weeks 35-37)
- Non-stress tests if indicated
Baby Size by Week: Fruit and Vegetable Comparisons
One of the most popular ways to visualize your baby's growth is comparing their size to familiar fruits and vegetables. Here is a week-by-week guide to baby's size throughout pregnancy:
First Trimester
| Week | Size Comparison | Length | Weight |
|---|---|---|---|
| 4 | Poppy seed | 0.1 cm | <1 g |
| 5 | Sesame seed | 0.2 cm | <1 g |
| 6 | Lentil | 0.5 cm | <1 g |
| 7 | Blueberry | 1.0 cm | <1 g |
| 8 | Raspberry | 1.6 cm | 1 g |
| 9 | Grape | 2.3 cm | 2 g |
| 10 | Kumquat | 3.1 cm | 4 g |
| 11 | Fig | 4.1 cm | 7 g |
| 12 | Lime | 5.4 cm | 14 g |
Second Trimester
| Week | Size Comparison | Length | Weight |
|---|---|---|---|
| 14 | Lemon | 8.7 cm | 43 g |
| 16 | Avocado | 11.6 cm | 100 g |
| 18 | Bell pepper | 14.2 cm | 190 g |
| 20 | Banana | 16.4 cm | 300 g |
| 22 | Papaya | 27.8 cm | 430 g |
| 24 | Cantaloupe | 30.0 cm | 600 g |
| 26 | Lettuce head | 35.6 cm | 760 g |
Third Trimester
| Week | Size Comparison | Length | Weight |
|---|---|---|---|
| 28 | Eggplant | 37.6 cm | 1.0 kg |
| 30 | Cabbage | 39.9 cm | 1.3 kg |
| 32 | Jicama | 42.4 cm | 1.7 kg |
| 34 | Cantaloupe | 45.0 cm | 2.15 kg |
| 36 | Romaine lettuce | 47.4 cm | 2.6 kg |
| 38 | Leek | 49.8 cm | 3.1 kg |
| 40 | Small pumpkin | 51.2 cm | 3.5 kg |
Note: These are average measurements. Individual babies may be larger or smaller and still be perfectly healthy.
Key Pregnancy Milestones Timeline
Throughout your pregnancy, several important milestones mark your baby's development. Here is a comprehensive timeline of what to expect and when:
First Trimester Milestones
Week 4-5: Implantation & Early Development
- Fertilized egg implants in uterine wall
- Pregnancy hormone (hCG) begins production
- Home pregnancy test may show positive
Week 5-6: Heartbeat Begins
- Baby's heart starts beating (80-100 bpm initially)
- May be visible on transvaginal ultrasound
- Neural tube (becomes brain and spine) is forming
Week 8: Major Organs Forming
- Heart, brain, lungs, liver, and kidneys developing
- Arm and leg buds appear
- Baby is now called an embryo
Week 10: End of Embryonic Period
- Baby officially becomes a "fetus"
- All major organs have begun development
- Tiny fingers and toes are visible
Week 12: End of First Trimester
- Risk of miscarriage drops significantly (to about 2%)
- Baby can make sucking movements
- Reflexes begin to develop
Second Trimester Milestones
Week 13: Second Trimester Begins
- Often called the "honeymoon" trimester
- Many women experience relief from nausea
- Baby's fingerprints are forming
Week 16: Gender May Be Visible
- External genitalia developed enough to see on ultrasound
- Baby is making facial expressions
- Sucking reflexes developing
Week 18-20: First Movements (Quickening)
- Most women feel first flutters or "butterflies"
- First-time moms may not notice until week 20-22
- Baby is developing sleep/wake cycles
Week 20: Anatomy Scan
- Detailed ultrasound checks all organs and development
- Baby's length measured from head to toe
- Halfway point of pregnancy!
Week 24: Viability Milestone
- Baby has approximately 50% survival chance if born now
- Survival improves rapidly each additional week
- Surfactant production begins in lungs
Third Trimester Milestones
Week 27: Third Trimester Begins
- Baby's eyes can open and close
- Responds to light and sound
- Brain developing rapidly
Week 28: Eyes Open
- Baby can blink and see light through uterine wall
- REM sleep cycles developing
- Immune system developing
Week 32: Practice Breathing
- Lungs practicing breathing movements
- Baby gaining about half a pound per week
- Bones hardening (except skull)
Week 36: Baby May Drop (Lightening)
- Baby's head may engage in pelvis
- Breathing may become easier
- Bathroom trips may increase
Week 37: Full Term
- Baby is considered full term
- Lungs are mature
- Baby is ready for life outside the womb
Week 40: Due Date
- Only 5% of babies arrive exactly on due date
- Most babies born within 2 weeks of due date
- Post-date monitoring begins if pregnancy continues
Accuracy of Due Date Calculations
Understanding the accuracy and limitations of due date calculations helps set realistic expectations for when your baby will arrive.
How Accurate is the Estimated Due Date?
Statistics on delivery timing:
- Only 5% of babies are born on their exact due date
- About 80% of babies are born within 2 weeks of the due date (38-42 weeks)
- 50% of first-time mothers deliver after their due date
- Average first-time pregnancy lasts about 41 weeks and 1 day
Factors Affecting Due Date Accuracy
Calculation Method:
| Method | Accuracy |
|---|---|
| LMP (standard) | +/- 5 days if cycles are regular |
| Early ultrasound (before week 9) | +/- 5 days |
| First trimester ultrasound (weeks 9-13) | +/- 7 days |
| Second trimester ultrasound | +/- 10-14 days |
| Third trimester ultrasound | +/- 21 days |
Why LMP-Based Dating May Be Inaccurate:
- Irregular menstrual cycles
- Uncertainty about exact LMP date
- Ovulation didn't occur on day 14
- Recent hormonal birth control use
- Breastfeeding when conception occurred
When Doctors May Adjust Your Due Date
Your healthcare provider may revise your due date based on ultrasound if:
- Early ultrasound measurements differ from LMP dating by more than 5-7 days
- LMP is unknown or uncertain
- Cycles are irregular
- Conception occurred through fertility treatment with known dates
The "Due Month" Concept
Many healthcare providers now prefer discussing a "due month" or "birth window" rather than a specific due date:
- Early term: 37 weeks 0 days - 38 weeks 6 days
- Full term: 39 weeks 0 days - 40 weeks 6 days
- Late term: 41 weeks 0 days - 41 weeks 6 days
- Post-term: 42 weeks 0 days and beyond
This approach reduces anxiety about "going overdue" and reflects the reality that healthy babies can safely arrive within a 5-week window.
Pro Tips
- 💡**Track your menstrual cycles before trying to conceive**: Knowing your typical cycle length helps calculate a more accurate due date. Apps or a simple calendar can help you track patterns over several months. Regular cycles make due date calculations more reliable.
- 💡**Remember that your due date is an estimate, not a deadline**: Only 5% of babies arrive on their exact due date. Think of it as a "due month" - most babies arrive within 2 weeks before or after the calculated date. This mindset reduces stress and unrealistic expectations.
- 💡**Attend your early prenatal appointments**: A first-trimester ultrasound (ideally before 13 weeks) provides the most accurate pregnancy dating. If your ultrasound-based date differs significantly from your LMP-based calculation, your provider may adjust your official due date.
- 💡**Prepare for baby to arrive anytime after 37 weeks**: While 40 weeks is the target, babies born anytime from 37 weeks are considered term. Have your hospital bag packed, car seat installed, and childcare arrangements for other children finalized by 36 weeks.
- 💡**Keep your healthcare provider informed if you have irregular cycles**: Let your doctor or midwife know if your cycles vary significantly in length (less than 21 days or more than 35 days). This information helps them interpret ultrasound findings and may lead to additional monitoring.
Frequently Asked Questions
This is one of the most confusing aspects of pregnancy dating. The 40-week pregnancy calculation starts from the first day of your last menstrual period (LMP), not from conception.
Here's why:
-
Historical reasons: Before ultrasound technology, the LMP was the only reliable date women could provide. Doctors couldn't determine exact conception dates.
-
Conception usually occurs 2 weeks after LMP: In a typical 28-day cycle, ovulation (and conception) happens around day 14. So when doctors say you're "4 weeks pregnant," your baby has actually only been developing for about 2 weeks.
-
Actual fetal age vs. gestational age:
- Gestational age: Counted from LMP (40 weeks total)
- Fetal age: Counted from conception (38 weeks total)
- Both refer to the same pregnancy duration, just different starting points
Practical example:
- LMP: January 1
- Likely conception: ~January 14 (2 weeks later)
- Due date: October 8 (280 days from LMP)
- Actual time baby develops: 266 days from conception
This system remains standard because the LMP is usually easier to remember than the exact conception date, and it provides a consistent framework for prenatal care worldwide.
