Pregnancy Due Date Calculator: When Will Your Baby Be Born?
The moment you see that positive pregnancy test, one question fills your mind:
"When will my baby arrive?"
Due date marks the end of your pregnancy journey — the day your baby is expected to be born. But pregnancy isn't an exact science. Your due date isn't set in stone; it's an educated guess with a ±2 week window.
This guide explains how due dates are calculated, what they actually mean, and how to use our pregnancy due date calculator to find yours.
How Pregnancy Due Date Is Calculated
Surprisingly, pregnancy isn't counted from conception. It's counted from your Last Menstrual Period (LMP) — the first day of your last period.
Why LMP?
- Most women don't know exact conception date
- LMP is easy to remember
- Medical standard worldwide
The Calculation
Pregnancy = 280 days (40 weeks) from LMP
To calculate due date manually:
- Take your LMP date
- Add 9 months
- Subtract 3 months (Naegele's rule)
- Add 7 days
Example:
- LMP: January 15
- Add 9 months = October 15
- Subtract 3 months = July 15
- Add 7 days = July 22 (due date)
Our calculator does this instantly and accurately, accounting for leap years and calendar variations.
What Your Due Date Actually Means
Here's something important: Your due date doesn't mean your baby will be born on that exact day.
Only about 5% of babies arrive on their exact due date!
The "Due Window"
A more accurate way to think about due date:
- 2 weeks before = earliest
- Due date = expected
- 2 weeks after = latest
Medical facts:
- Babies arriving 37-42 weeks: Normal
- Before 37 weeks: Premature
- After 42 weeks: Overdue (doctor intervention)
What's Normal
| Timeline |
Name |
% of Pregnancies |
Status |
| <37 weeks |
Preterm |
8-10% |
Early |
| 37-42 weeks |
Term |
85-90% |
Normal |
| >42 weeks |
Post-term |
1-2% |
Late |
Most pregnancies naturally deliver between 38-41 weeks.
How Pregnancy Is Dated: The Trimester Breakdown
Pregnancy is divided into 3 trimesters of roughly 13-14 weeks each.
First Trimester (Weeks 1-13)
What happens:
- Egg implants in uterus
- Heart, brain, organs start developing
- You start gaining weight (1-3 kg)
Your symptoms:
- Morning sickness (peaks week 6-9)
- Fatigue
- Breast tenderness
- Mood swings
Medical checkups:
- Confirm pregnancy
- Dating ultrasound (week 8-12)
- Blood tests for risk screening
Second Trimester (Weeks 14-27)
What happens:
- Baby grows rapidly
- You start showing
- Baby's gender visible on ultrasound
Your symptoms:
- Nausea reduces
- Energy returns
- Kick/movement felt (week 16-20)
- Back pain starts
Medical checkups:
- Anatomy ultrasound (most important)
- Glucose screening test
- Regular checkups
Third Trimester (Weeks 28-40)
What happens:
- Baby gains 50% of birth weight
- Baby moves to head-down position
- Contractions start (Braxton-Hicks)
Your symptoms:
- Frequent urination
- Swelling in legs/feet
- Difficulty sleeping
- Pre-labor signs (mucus plug loss, "dropping")
Medical checkups:
- Biweekly, then weekly checkups
- Monitor blood pressure
- Check baby's position
- Fetal stress tests
Our Pregnancy Due Date Calculator: How It Works
Our calculator uses Naegele's rule, the standard medical method:
Formula: LMP + 280 days = Due date
What you need to provide:
- First day of your last menstrual period
What we calculate:
- Your current pregnancy week
- Your due date
- Days until due date
- Your current trimester
- Conception date (approximate)
- Baby's age in weeks and days
Everything is done in your browser — your data is never stored.
How Accurate Is Your Due Date?
| Method |
Accuracy |
Error Range |
| LMP |
95% |
±14 days |
| Early ultrasound (8-13 weeks) |
98% |
±3-5 days |
| Mid ultrasound (14-20 weeks) |
95% |
±7-10 days |
| Late ultrasound (>20 weeks) |
85% |
±14-21 days |
Early ultrasound is most accurate. If your LMP date and ultrasound date differ by >1 week, doctors use the ultrasound date.
Signs Your Baby Is Coming
Weeks 36-39: Preparation Signs
- Dropping/lightening: Baby moves lower in pelvis (you can breathe easier!)
- Braxton-Hicks: Practice contractions (irregular, painless)
- Diarrhea: Bowels preparing to empty
- Joint pain: Ligaments loosening for delivery
Week 40+: Pre-Labor Signs
- Bloody show: Mucus plug loss (pink/brown discharge)
- Regular contractions: 5-1-1 rule = pain every 5 min, lasting 1 min, for 1+ hour
- Water breaking: Amniotic fluid leaks/gushes
- Extreme nesting: Urge to clean, prepare
- Weight loss: Losing 0.5-1 kg in last week
When to Go to Hospital
Call your doctor/hospital if:
- Contractions every 5 minutes, regular for 1+ hour
- Water breaks (with or without contractions)
- Heavy bleeding (more than period)
- Severe abdominal pain
- Dizziness/fainting
- No fetal movement for 2+ hours
Preparing for Your Due Date
4 Weeks Before Due Date (Week 36)
- ✓ Pack hospital bag
- ✓ Install car seat
- ✓ Arrange maternity leave
- ✓ Stock frozen meals
2 Weeks Before Due Date (Week 38)
- ✓ Final prenatal checkup
- ✓ Confirm pediatrician
- ✓ Arrange postpartum help
- ✓ Mentally prepare
1 Week Before Due Date (Week 39)
- ✓ Rest, walk (avoid strenuous exercise)
- ✓ Monitor Braxton-Hicks
- ✓ Stay within 30 min of hospital
- ✓ Avoid long travels
Due Date Week (Week 40)
- ✓ Keep checkup appointments
- ✓ Know pre-labor signs
- ✓ Have hospital number saved
- ✓ Remain calm (baby will come!)
Frequently Asked Questions
Q: Can my due date change?
A: Yes. If early ultrasound shows different date from LMP, doctors use ultrasound date.
Q: What if I have irregular cycles?
A: Ultrasound dating is more accurate than LMP calculation. Get a dating scan by 13 weeks.
Q: Do I have to deliver on my due date?
A: No. Only 5% deliver on exact due date. Most deliver within 2 weeks before/after.
Q: Should I induce labor on my due date?
A: No. Doctors only induce if you're 41+ weeks or complications exist.
Q: Does due date affect Zodiac sign?
A: Your zodiac is based on birth date, not due date. Some babies arrive weeks early/late, changing zodiac signs!
Bottom Line
Your due date is your pregnancy milestone, but not a deadline. Babies arrive on their own schedule within a 2-week window around the due date.
Use our pregnancy due date calculator to find when your baby might arrive, then focus on staying healthy, managing stress, and preparing for the beautiful journey ahead.
Congratulations on your pregnancy! 👶