Pregnancy Due Date Calculator: Complete Guide + Free Tool (2025)

Expecting a baby? One of the first questions every pregnant woman asks is: “When is my baby due?” Our pregnancy due date calculator uses three clinically validated methods to estimate your delivery date—whether you know your last menstrual period (LMP), conception date, or had an ultrasound. Get instant results plus your complete trimester timeline.

📅 Pregnancy Due Date Calculator

How Is Pregnancy Due Date Calculated?

Pregnancy typically lasts 40 weeks (280 days) from the first day of your last menstrual period. However, only about 5% of babies are born exactly on their due date. Understanding the calculation methods helps you know what to expect.

1. Naegele’s Rule (LMP Method)

The most common calculation method used by healthcare providers:

Due Date = First Day of LMP + 1 year − 3 months + 7 days

For cycles longer or shorter than 28 days, add or subtract the difference:

Adjusted Due Date = Standard Due Date + (Cycle Length − 28 days)

2. Conception Date Method

If you know your conception date (e.g., through IVF tracking or ovulation monitoring):

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

3. Ultrasound Dating

First-trimester ultrasounds (weeks 8-13) are the most accurate for dating pregnancy. The ultrasound measures:

• Crown-rump length (CRL): Baby’s length from head to bottom
• Gestational sac size: Early pregnancy measurement

Ultrasound dating becomes less accurate after the first trimester as babies grow at different rates.

Pregnancy Timeline: What to Expect Each Trimester

Important Milestones During Pregnancy

Key Tests and Screenings

• Week 8-12: First prenatal visit, blood tests, dating ultrasound
• Week 10-13: Nuchal translucency screening (Down syndrome risk)
• Week 15-20: Quad screen, amniocentesis (if indicated)
• Week 18-22: Anatomy ultrasound (detailed organ check)
• Week 24-28: Glucose challenge test (gestational diabetes)
• Week 35-37: Group B strep screening

Viability Milestones

• Week 24: Age of viability—baby has a chance of survival outside womb with intensive care
• Week 28: Third trimester begins—90% survival rate with medical intervention
• Week 37: Full term—baby is considered fully developed
• Week 40: Estimated due date
• Week 42: Post-term—induction usually recommended

Frequently Asked Questions

How accurate is a due date calculator?

Due date calculators provide an estimate, not a guarantee. Only about 5% of babies are born on their exact due date. Most deliveries occur within two weeks before or after the estimated date. First-trimester ultrasound dating is the most accurate method.

Can my due date change?

Yes. Your healthcare provider may adjust your due date based on:

• First-trimester ultrasound measurements
• Fundal height measurements (uterus size)
• Irregular periods or uncertain LMP

What if I don’t remember my last period?

If you can’t recall your LMP, your doctor will use:

• Early ultrasound dating (most accurate)
• Physical examination and fundal height
• First fetal movements felt (quickening, typically week 18-20)

Is my due date different with IVF?

Yes. With IVF, conception date is known precisely. Your due date is calculated as:

• Day 3 embryo transfer: Due date = Transfer date + 263 days
• Day 5 embryo transfer: Due date = Transfer date + 261 days

What happens if I go past my due date?

Going to 41-42 weeks is common. Your doctor will:

• Monitor baby more frequently (non-stress tests, biophysical profiles)
• Check amniotic fluid levels
• Consider induction at 41-42 weeks to reduce risks

Factors That Can Affect Your Due Date

Try Our Other Pregnancy Calculators

Planning for your baby’s arrival involves many calculations. Check out these related tools:

• APGAR Score Calculator – Assess newborn health immediately after birth
• eGFR Calculator – Monitor kidney function during pregnancy (important for pre-eclampsia screening)

Conclusion

Knowing your estimated due date helps you prepare for your baby’s arrival and track important milestones throughout pregnancy. While our calculator provides a reliable estimate based on clinically validated methods, remember that every pregnancy is unique.

Key takeaways:

• Use the LMP method if you have regular 28-day cycles
• Ultrasound dating in the first trimester is most accurate
• Only 5% of babies arrive on their exact due date
• Regular prenatal care is essential regardless of your estimated date

📌 Bookmark this calculator to track your pregnancy progress, and congratulations on this exciting journey!

Medical Disclaimer: This pregnancy due date calculator is for educational and informational purposes only. It does not constitute medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider for prenatal care and personalized medical guidance. Due dates are estimates, and individual pregnancies vary. If you have concerns about your pregnancy, contact your doctor or midwife promptly.