Pregnancy Due Date Calculator
Get an accurate estimate of your due date and track important pregnancy milestones
Enter Your Date
First Day of Last Period
Calculation Method
Select how you want to calculate your due date
Last Period
Standard method using your last menstrual period
Conception
Calculate from known conception date
IVF Transfer
Based on embryo transfer date
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Age Calculator
Calculate exact age and time between any two dates
Date Calculator
Calculate duration between dates and add/subtract time periods
Understanding Your Pregnancy Journey
A comprehensive guide through the three trimesters of pregnancy
First Trimester
Second Trimester
Third Trimester
Last Menstrual Period and Naegele's Rule
The traditional starting point for due date calculation
The most common starting point is the first day of your last menstrual period (LMP). Naegele's Rule is the traditional calculation: add 7 days, subtract 3 months, and add 1 year to the LMP date. This is equivalent to adding 280 days (40 weeks) from the LMP.
Naegele's Rule Visual Calculator
Assumptions
Limitations
Conception-Date-Based Calculation
When the exact fertilization date is known
If the exact date of conception (fertilization) is known (for example via fertility tracking or insemination), one can calculate the due date by adding 266 days (38 weeks) to the conception date. This is because conception typically occurs about 14 days after the first day of LMP, so 280 – 14 = 266.
Conception Date Formula
Usage and Reliability
This method is used mainly when fertilization is precisely known (e.g., ovulation tracking, intrauterine insemination). However, pinpointing conception is difficult: sperm can live ~5 days in the reproductive tract and ovulation lasts ~24 hours, so intercourse around the fertile window only gives an approximate conception date.
First-Trimester Ultrasound Dating
The gold standard for pregnancy dating accuracy
An early ultrasound (usually 6–12 weeks) is the most accurate way to date a pregnancy. In the first trimester, the sonographer measures the embryo's crown–rump length (CRL). Established charts convert that measurement into gestational age. The accuracy of first-trimester ultrasound dating is ±5–7 days.
When Used
- • Routinely at first prenatal visit (8–12 weeks)
- • When LMP is unknown or unreliable
- • For irregular menstrual cycles
- • To confirm or adjust initial dating
Clinical Guidelines
- • ACOG recommends adjusting due date if ≥7-day discrepancy
- • NHS advises 12-week scan for accurate dating
- • Later ultrasounds (2nd trimester) less precise (±10–14 days)
- • Usually doesn't override established first-trimester date
Reliability
Very high in early pregnancy. Because measurement error is small in the first trimester, an ultrasound-based date is generally considered the best obstetric estimate. This method is preferred when other dating methods are uncertain.
IVF and Assisted Reproduction Dating
Precise dating when fertilization and embryo age are known
Pregnancies from in vitro fertilization (IVF) or similar assisted reproductive technologies can be dated precisely, since fertilization and embryo age are known. The due date is calculated from the embryo transfer date plus a set number of days:
Day-5 Embryo (Blastocyst)
EDD = Transfer Date + 261 days
Example: Day-5 embryo transferred January 10, 2025 → Due date around September 27, 2025
Day-3 Embryo
EDD = Transfer Date + 263 days
This calculation accounts for the exact embryo development stage at transfer
Precision Advantage
Because the exact age of the embryo and fertilization date are known, IVF-based dating is very precise. This matches ACOG recommendations that IVF dates use the known embryo age. Multiple embryo transfers or thawed embryos follow the same rules based on their development stage.
Comparison of Dating Methods
Accuracy and reliability of different calculation approaches
LMP / Naegele's Rule
Conception Date
Ultrasound (1st Trimester)
IVF / ART Dating
Accuracy Comparison
Important Note: These examples assume a 28-day cycle unless noted. Real due dates will vary; only about 5% of babies arrive on the exact EDD. Multiple data points are often used for the most accurate dating.
When to Recalculate or Adjust
Understanding when and why due dates change
Because any due date is an estimate, it may change with new information. For instance, if an early ultrasound shows the fetus is smaller or larger than expected for the LMP date, the provider will often revise the EDD to match the ultrasound-based gestational age. This is common and does not indicate a problem—updating the due date ensures more accurate timing of care.
Common Reasons for Adjustment
- • Ultrasound shows different gestational age
- • Irregular or unknown menstrual cycles
- • Uncertain LMP recall
- • Significant discrepancy between methods
Clinical Standards
- • ACOG notes dating is "suboptimal" without early ultrasound
- • First ultrasound (8–12 weeks) becomes "best obstetric estimate"
- • Multiple data points used for most accurate dating
- • Ensures proper timing of prenatal care
Summary
LMP/Naegele's rule provides a quick first estimate of 280 days (40 weeks) from LMP. First-trimester ultrasound (CRL) is the gold-standard for dating when available. In IVF pregnancies, the embryo transfer date with the embryo's age determines the EDD very precisely. Each method has limitations, so obstetricians often use multiple data points to arrive at the most accurate due date.
Health & Wellness During Pregnancy
Nutrition Guidelines
- • Increase caloric intake by 300-500 calories
- • Take prenatal vitamins with folic acid
- • Eat plenty of fruits and vegetables
- • Stay well hydrated
Safe Exercise
- • Walking and swimming are excellent choices
- • Maintain moderate activity levels
- • Listen to your body
- • Stay cool and hydrated
Common Pregnancy Questions
Answers to frequently asked questions about pregnancy
Detecting Pregnancy
Early signs and methods of pregnancy detection
Early Signs
Physical Signs
- • Missed period
- • Morning sickness
- • Breast tenderness
- • Fatigue
- • Frequent urination
Emotional Changes
- • Mood swings
- • Food aversions or cravings
- • Heightened emotions
Detection Methods
Home Testing
- • Home pregnancy tests
- • Best time to test
- • Test accuracy rates
Medical Confirmation
- • Blood tests
- • First ultrasound
- • Doctor's consultation
Essential Prenatal Care
Medical Check-ups
- First trimester: Monthly visits
- Second trimester: Bi-weekly
- Third trimester: Weekly visits
Important Screenings
- Genetic testing options
- Ultrasound scans
- Blood work and monitoring
Vaccinations
- Flu shot
- Tdap vaccine
- Covid-19 vaccination
Important Lifestyle Changes
Essential adjustments for a healthy pregnancy
What to Do
- Take prescribed prenatal vitamins
- Get adequate rest and sleep
- Stay physically active as approved
- Maintain good hygiene
What to Avoid
- Smoking and alcohol
- Raw or undercooked foods
- Excessive caffeine
- High-risk activities
Common Pregnancy Concerns
Solutions and management strategies for common pregnancy symptoms
Morning Sickness
Back Pain
Sleep Issues
Heartburn
Swelling
Mood Changes
When to Contact Your Healthcare Provider Immediately
Preparing for Birth
Essential preparations for labor and delivery
Birth Plan
- Choose delivery location
- Pain management preferences
- Support person choices
- Emergency procedures
Hospital Bag
- Important documents
- Comfort items
- Baby essentials
- Personal care items
Labor Signs
- Contractions timing
- Water breaking
- Warning signs
- When to go to hospital
References & Sources
Authoritative sources supporting due date calculation methods
[1] American College of Obstetricians and Gynecologists (ACOG)
"Methods for Estimating the Due Date." Clinical practice guidelines for pregnancy dating, ultrasound timing, and gestational age assessment.ACOG Guidelines
[2] Hopkins Medicine
"Calculating a Due Date." Educational resources on Naegele's Rule, pregnancy duration, and due date estimation methods.Hopkins Pregnancy Guide
[3] Cleveland Clinic
"Pregnancy: Calculating Your Due Date." Medical information on conception dating, ultrasound accuracy, and pregnancy timeline calculations.Cleveland Clinic
[4] Evidence Based Birth
"Evidence on Due Dates." Research-based analysis of due date calculation methods, accuracy rates, and clinical evidence.Evidence Based Birth
[5] Better Health Victoria
"Pregnancy and Birth: Due Dates." Australian health department guidelines on pregnancy dating and delivery timing expectations.Better Health Victoria
[6] NHS (National Health Service)
"Your Pregnancy and Baby Guide." UK national health service guidance on pregnancy dating, ultrasound scans, and prenatal care timing.NHS Pregnancy Guide
Medical Disclaimer
These calculations are based on established obstetric guidelines and should be used in consultation with healthcare providers. Individual pregnancy timelines vary significantly, and all dating decisions should be made under medical supervision. This calculator is for educational purposes and should not replace professional prenatal care.