Pregnancy Due Date Calculator
Calculate your estimated due date using your last menstrual period with Naegele's Rule
Enter the first day of your last menstrual period
Average cycle length is 28 days
Key Pregnancy Milestones
Trimester Overview
Due dates are estimates. Babies can arrive 2 weeks before or after the calculated date.
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Understanding Pregnancy Dating
Learn how pregnancy due dates are calculated and what to expect during your pregnancy journey
Pregnancy is measured from the first day of your last menstrual period (LMP), not from conception.
Only about 5% of babies are born on their exact due date. Most arrive within 2 weeks of the estimate.
The standard method adds 280 days (40 weeks) to your LMP to calculate the estimated due date.
Babies born between 37-42 weeks are considered full term. This is a 5-week window around your due date.
Your healthcare provider may adjust your due date based on ultrasound measurements and other factors.
Pregnancy is divided into three trimesters, each lasting about 13-14 weeks, for a total of 40 weeks.
Pregnancy Timeline
- Week 1-4Implantation and early development
- Week 5-8Organ formation begins
- Week 9-12End of first trimester
- Week 13-27Second trimester growth
- Week 28-40Final development and birth
When to See Your Doctor
- • Schedule first appointment around 8-10 weeks
- • Regular prenatal visits throughout pregnancy
- • Important screenings at specific weeks
- • Contact immediately for concerning symptoms
- • Discuss birth plan in third trimester
Disclaimer: This calculator provides estimates based on standard medical calculations. Every pregnancy is unique, and you should always consult with your healthcare provider for personalized medical advice and care throughout your pregnancy.
How Due Dates Are Calculated
Different methods for calculating pregnancy due dates, each with varying levels of accuracy
The most common method used by healthcare providers worldwide
- •Based on a 28-day menstrual cycle
- •Assumes ovulation on day 14
- •Adds 280 days to LMP date
- •Can be adjusted for different cycle lengths
Uses ultrasound measurements to estimate gestational age
- •Most accurate in first trimester
- •Measures crown-rump length
- •Can override LMP dating
- •Standard medical practice
Calculates from known ovulation date instead of LMP
- •More accurate than LMP method
- •Requires ovulation tracking
- •Adds 266 days to ovulation
- •Good for irregular cycles
Precise dating for IVF pregnancies based on embryo transfer
- •Most accurate method available
- •Based on exact fertilization date
- •Accounts for embryo development stage
- •Used for assisted reproduction
| Method | Accuracy | Best Used When | Limitations |
|---|---|---|---|
| Naegele's Rule | ±2 weeks | Regular 28-day cycles | Assumes standard cycle |
| Ultrasound | ±3-5 days (early) | First trimester | Less accurate later |
| Ovulation-Based | ±1 week | Known ovulation date | Requires tracking |
| IVF Dating | ±2-3 days | IVF pregnancies | Only for assisted reproduction |
Clinical Practice
In clinical practice, healthcare providers often use a combination of methods. They may start with Naegele's Rule based on LMP, then confirm or adjust the due date using early ultrasound measurements. The most accurate dating is typically achieved with first-trimester ultrasounds.
Frequently Asked Questions
Common questions about pregnancy due date calculations and what to expect
Prenatal Care Timeline
- • 8-10 weeks: First prenatal visit
- • 11-14 weeks: First trimester screening
- • 18-22 weeks: Anatomy ultrasound
- • 24-28 weeks: Glucose screening
- • 36+ weeks: Group B strep test
Warning Signs to Watch For
- • Severe abdominal pain
- • Heavy bleeding
- • Severe headaches
- • Vision changes
- • Decreased fetal movement
Important: This calculator is for informational purposes only and should not replace professional medical advice. Always consult with your healthcare provider for personalized pregnancy care and any concerns about your pregnancy.