Advertisement Space
Pregnancy Due Date Calculator
Most Common Method: Used by 95% of healthcare providers
Note: Ovulation typically occurs 12-16 days after LMP
±1-2 weeks in second trimester
±2-3 weeks in third trimester
Your Due Date Information
-
Pregnancy Trimesters
First Trimester
Weeks 1-13
Rapid development
Second Trimester
Weeks 14-26
Quickening & growth
Third Trimester
Weeks 27-40
Final preparation
Understanding Your Pregnancy Timeline
How Pregnancy Dating Works
Pregnancy is dated from the first day of your last menstrual period (LMP), even though conception actually occurs about 2 weeks later. This is why pregnancy is said to last 40 weeks (280 days) from LMP, but only about 38 weeks (266 days) from conception.
The Three Trimesters
First Trimester (Weeks 1-13)
- Week 1-2: Egg and sperm meet, fertilization occurs
- Week 3-4: Embryo implants in uterus
- Week 5-8: Heart, brain, and major organs form
- Week 9-13: Fetus becomes recognizable, morning sickness common
- Changes: Nausea, fatigue, breast tenderness, frequent urination
Second Trimester (Weeks 14-26)
- Week 14-18: Sex can be determined, morning sickness usually ends
- Week 19-22: Quickening felt (baby movements)
- Week 23-26: Baby becomes more active, hearing develops
- Changes: Energy returns, "pregnancy glow," baby bump appears
- Milestone: 20-week ultrasound (anatomy scan)
Third Trimester (Weeks 27-40)
- Week 27-30: Baby gains significant weight, fetal movements visible
- Week 31-36: Baby moves to head-down position for delivery
- Week 37-40: Baby considered full-term, ready for birth
- Changes: Difficulty sleeping, back pain, Braxton Hicks contractions
- Milestone: Birth between 37-42 weeks is considered term
Due Date Calculation Methods & Accuracy
LMP Method (Naegele's Rule)
- Accuracy: ±2 weeks (standard deviation)
- Assumes: 28-day cycle, ovulation on day 14
- Used by: 95% of healthcare providers as initial method
- Best for: Women with regular, predictable cycles
Conception/Ovulation Method
- Accuracy: ±3 days if conception date is known
- Used when: Conception date is known or tracked
- Calculation: Ovulation = LMP + 14 days (approximately)
- Best for: Assisted reproductive technology (ART) pregnancies
Ultrasound Dating
- Accuracy: ±3-5 days in first trimester
- Accuracy: ±1-2 weeks in second trimester
- Accuracy: ±2-3 weeks in third trimester
- Most Accurate: First trimester ultrasound
- Best for: Confirming or adjusting LMP-based dates
Which Method is Most Accurate?
- 1st Trimester Ultrasound: Most accurate (±3-5 days)
- Known Conception Date: Very accurate (±3 days)
- LMP with Regular Cycle: Accurate (±2 weeks)
- 2nd Trimester Ultrasound: Moderate (±1-2 weeks)
- 3rd Trimester Ultrasound: Least accurate (±2-3 weeks)
Important Pregnancy Information
What is Normal Pregnancy Duration?
- Full Term: 37-42 weeks (259-294 days)
- Early Term: 37-38 weeks
- Full Term: 39-40 weeks (ideal)
- Late Term: 41-42 weeks
- Preterm: Before 37 weeks
- Post-term: After 42 weeks
Delivery Window (Due Date ±2 weeks)
Your baby is considered "full-term" at 37 weeks. Most hospitals will not induce labor before 39 weeks unless there's a medical reason. Labor can begin anytime between 37-42 weeks and is considered normal.
When Should Labor Be Induced?
- 42 weeks: Post-term pregnancy (health risks increase)
- Complications: Preeclampsia, gestational diabetes, infection
- Medical Reasons: Maternal or fetal health concerns
- Medical Decision: Always consult your healthcare provider
Frequently Asked Questions
Is my due date exact?
No. Your due date is an estimate. Only about 4% of babies are born on their actual due date. Most babies arrive within 2 weeks before or after the due date (37-42 weeks).
What if I don't know my LMP?
If you're unsure about your LMP, your healthcare provider will order an early ultrasound (first trimester) which is the most accurate dating method. This is very accurate within ±3-5 days.
Can my due date change?
Yes. If an ultrasound shows your pregnancy is further along or behind than your LMP date suggests, your healthcare provider may adjust your due date. This is common and normal.
What happens if I go past my due date?
Most babies born after the due date are fine. However, at 42 weeks, risks increase. Your doctor may recommend induction. Labor after 39 weeks is considered normal and low-risk.
How is gestational age calculated?
Gestational age = weeks since first day of LMP. At 40 weeks gestational age, the baby is born. Babies are usually born between 37-42 weeks gestational age (preterm to post-term).
What if I have irregular periods?
If your cycles are irregular, an early ultrasound is more accurate for dating. The first trimester ultrasound is accurate within ±3-5 days, regardless of cycle regularity.
Is there an ideal time to give birth?
39 weeks is considered ideal (full term). At this age, baby's lungs are fully developed. While births from 37 weeks are considered safe, waiting until 39 weeks provides best outcomes for baby's health.
Can I calculate when baby was conceived?
Conception typically occurs about 14 days after the first day of LMP (during ovulation). However, this varies. This calculator can show the range of likely conception dates.
Related Calculators & Tools
Explore our other health and pregnancy calculators: