Due Date Calculator | Pregnancy Due Date Estimator

📖 How to Use This Due Date Calculator

Select your calculation method - Choose from LMP, Conception Date, or Ultrasound.

Enter the date - Input your LMP, conception date, or known due date.

Click "Calculate Due Date" - Get your estimated due date, current pregnancy week, trimester, and milestones.

🤰 How Pregnancy Due Dates Are Calculated

A full-term pregnancy typically lasts about 280 days (40 weeks) from the first day of your last menstrual period (LMP). Conception usually occurs around day 14 of a 28-day cycle, which is why due dates are calculated 40 weeks from LMP but only 38 weeks from conception.

Naegele's Rule is the standard method for calculating due dates: Due Date = LMP + 280 days. This method assumes a regular 28-day cycle with ovulation on day 14. Only about 4-5% of babies are actually born on their exact due date - most arrive between 37 and 42 weeks.

📊 Calculation Methods Explained

LMP Method: Due Date = LMP + 280 days (40 weeks). Most common method for women with regular 28-day cycles.
Conception Date Method: Due Date = Conception Date + 266 days (38 weeks). Useful when conception date is known (IVF or tracked ovulation).
Ultrasound Method: First-trimester ultrasounds (8-12 weeks) provide the most accurate dating. Measurements of the fetus determine gestational age within 3-5 days accuracy.

📅 Pregnancy Trimesters

First Trimester (Weeks 1-12): Morning sickness, fatigue, hormonal changes. Baby's major organs form. First ultrasound between 8-12 weeks.
Second Trimester (Weeks 13-26): Energy returns, baby movement felt (quickening around 18-22 weeks). Anatomy scan at 18-22 weeks.
Third Trimester (Weeks 27-40): Baby grows rapidly, prepare for delivery. Braxton Hicks contractions may occur. Hospital bag preparation recommended after 36 weeks.

💡 Important Pregnancy Milestones

Week 6-8: First heartbeat detected via ultrasound
Week 10-12: Nuchal translucency screening for chromosomal abnormalities
Week 16-20: Anatomy scan to check baby's development
Week 24-28: Gestational diabetes screening
Week 36-37: Group B Strep screening
Week 39-41: Full term - baby can arrive any day

❓ Frequently Asked Questions (FAQ)

How accurate is the due date calculator?

Due date calculations based on LMP have an accuracy of ±7-10 days. First-trimester ultrasound (8-12 weeks) is most accurate, with ±3-5 days accuracy. Only about 5% of babies are born on their exact due date.

What if my cycle is longer or shorter than 28 days?

For cycles longer than 28 days, ovulation occurs later - add the difference to your due date. For shorter cycles, subtract the difference. For example, a 35-day cycle would add 7 days to the due date.

When should I have my first ultrasound?

Most healthcare providers recommend the first ultrasound between 8-12 weeks. This confirms the pregnancy, checks for heartbeat, and provides the most accurate dating for your due date.

What is considered full term?

Early term: 37-38 weeks; Full term: 39-40 weeks; Late term: 41 weeks; Post-term: 42+ weeks. Babies born at 39-40 weeks have the best health outcomes.

Can I have a due date after 40 weeks?

Yes, due dates are estimates. Many providers allow pregnancy to continue until 41-42 weeks if mother and baby are healthy. Induction may be recommended after 41 weeks to reduce risks.

Why does due date change after ultrasound?

Early ultrasounds measure the baby's size (crown-rump length), which is very accurate for dating. If there's a discrepancy of more than 5-7 days from LMP calculation, the ultrasound date is typically used.