Pregnancy Due Date Calculator
Calculate your estimated due date and track your pregnancy week-by-week with important milestones and development stages.
Your due date and pregnancy timeline will appear here.
How to Use the Due Date Calculator
- Choose Calculation Method:
- Last Period: Most common - uses first day of your last menstrual period
- Conception Date: If you know exactly when conception occurred
- Ultrasound: Most accurate - uses measurements from dating scan
- Enter Date: Provide the required date based on your chosen method
- Calculate: See your due date, current week, and pregnancy milestones
Understanding Due Date Calculations
Naegele's Rule (LMP Method)
The most common calculation method, developed in the 1800s:
Due Date = LMP + 280 days (40 weeks)
Or: LMP + 1 year - 3 months + 7 days
Why 40 Weeks from Last Period?
Pregnancy is dated from the first day of your last menstrual period, even though conception typically occurs about 2 weeks later. This is because the LMP date is more reliably known than conception date.
- Week 1-2: Not actually pregnant yet (period and ovulation phase)
- Week 3: Conception occurs
- Week 4: Implantation
- Week 40: Full term, due date
Pregnancy Milestones by Trimester
First Trimester (Weeks 1-13)
- Week 4-5: Positive pregnancy test possible
- Week 6-7: Heartbeat detectable on ultrasound
- Week 8: Baby called "fetus" (no longer embryo)
- Week 12: End of first trimester, miscarriage risk drops significantly
- Week 13: First trimester screening (NT scan)
Mom: Morning sickness, fatigue, frequent urination, breast tenderness
Second Trimester (Weeks 14-27)
- Week 16-20: Feel baby's movements (quickening)
- Week 18-22: Anatomy scan (20-week ultrasound)
- Week 20: Halfway point!
- Week 24: Viability (baby could survive with medical support)
- Week 26-28: Glucose screening test
Mom: Energy returns, "pregnancy glow," baby bump shows, less nausea
Third Trimester (Weeks 28-40+)
- Week 32: Baby's position becomes important
- Week 36: Group B strep test
- Week 37: Early term - baby fully developed
- Week 39-40: Full term
- Week 40: Due date (only 5% deliver on this exact day!)
- Week 41-42: Post-term, likely to be induced
Mom: Braxton Hicks contractions, difficulty sleeping, frequent bathroom trips, nesting instinct
When Will Baby Actually Arrive?
Your due date is an estimate, not a deadline. Statistics show:
- Only 5% of babies are born on their exact due date
- 70% are born within 10 days of the due date
- 80% are born between weeks 38-42
- First babies tend to arrive slightly later (avg 40 weeks + 5 days)
- Subsequent babies tend to arrive earlier (avg 40 weeks + 3 days)
Full Term Definitions
| Classification | Gestational Age | Notes |
|---|---|---|
| Premature | Before 37 weeks | May need NICU support |
| Early Term | 37-38 weeks | Fully developed but not optimal |
| Full Term | 39-40 weeks | Ideal timing |
| Late Term | 41 weeks | May be monitored more closely |
| Post Term | 42+ weeks | Typically induced |
Frequently Asked Questions
Which calculation method is most accurate?
Ultrasound (especially first trimester) is most accurate. Early ultrasounds (before 13 weeks) can date pregnancy within 3-5 days. Second-trimester ultrasounds are less accurate (±1-2 weeks). If your ultrasound date differs significantly from LMP date, your doctor will likely use the ultrasound date.
What if I have irregular periods?
LMP-based calculations assume 28-day cycles and are less accurate with irregular cycles. An early ultrasound (dating scan) at 8-13 weeks provides the most reliable due date. Some women also track ovulation with tests or basal body temperature, which helps pinpoint conception.
Can my due date change?
Yes, especially if early ultrasound shows a different date than LMP calculation. Doctors typically adjust the due date only once, based on the earliest ultrasound. Later ultrasounds don't change the due date because babies grow at different rates.
Why is pregnancy 40 weeks, not 9 months?
40 weeks = 280 days ≈ 9 months + 1 week. It's easier to track by weeks than months. Some months have 4 weeks, others 4.5 weeks, making month-based tracking confusing. Medical professionals use weeks for precision.
What happens if I go past my due date?
Most doctors induce labor between 41-42 weeks. Going past 42 weeks increases risks (placental aging, low amniotic fluid). You'll have more frequent monitoring (NST, amniotic fluid checks) after 40 weeks. Many women opt for induction at 41 weeks.
How early can I find out if I'm pregnant?
Most home pregnancy tests work from the first day of a missed period (about 14 days after conception, or 4 weeks from LMP). Some sensitive tests work 6-8 days after ovulation. Blood tests (hCG) can detect pregnancy even earlier, around 9-11 days after conception.
What's the difference between gestational age and fetal age?
Gestational age: Calculated from LMP, what doctors use (e.g., "10 weeks pregnant"). Fetal age: Actual age since conception, about 2 weeks less. When someone says "10 weeks pregnant," the fetus is actually about 8 weeks old.
🤰 Important Pregnancy Milestones
- Week 8-13: First prenatal visit, dating ultrasound, genetic screening options
- Week 11-14: NT scan (nuchal translucency) and first-trimester screening
- Week 15-20: Quad screen or NIPT (genetic testing)
- Week 18-22: Anatomy scan (20-week ultrasound, find out sex)
- Week 24-28: Glucose tolerance test (gestational diabetes screening)
- Week 35-37: Group B strep test
- Week 36+: Weekly appointments begin
Preparing for Your Due Date
Pack Hospital Bag by Week 36: Include insurance cards, comfortable clothes, toiletries, phone charger, and baby's going-home outfit.
Install Car Seat Early: Have it inspected by a certified technician before week 37. Many hospitals won't let you leave without one properly installed.
Have a Birth Plan (but Stay Flexible): Discuss preferences with your doctor, but remember that plans often change during labor. Focus on baby's and your safety above all.
Know Labor Signs: Contractions (regular, increasing in intensity), water breaking, bloody show, and extreme pressure. Call your doctor when contractions are 5 minutes apart, lasting 1 minute each, for 1+ hour.
This calculator provides estimates for educational purposes only. Due dates are estimates, not exact predictions. Only 5% of babies are born on their due date. Always consult with your healthcare provider for medical advice, prenatal care, and monitoring. This tool does not replace professional medical consultation.