Estimated Due Date (EDD) Calculator
Calculate your estimated delivery date using multiple clinical methods: Naegele's rule (LMP + 280 days), Parikh's formula (cycle-adjusted), or ultrasound CRL/BPD measurements for trimester-specific accuracy.
Sample Scenarios
📅 LMP - Regular Cycle
Standard Naegele dating with 28-day cycle
✅ Multiple Methods
LMP and ultrasound within 5 days
🔬 IVF Precision
Most accurate from transfer date
⚠️ Dating Discrepancy
LMP and US differ 10+ days
🎯 Known Conception
Ovulation tracked with OPKs
🔬 First Trimester US
Most accurate ultrasound dating
Dating Methods
LMP
Current
⚠️For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
What is an EDD Calculator?
Calculate your estimated delivery date using multiple clinical methods: Naegele's rule (LMP + 280 days), Parikh's formula (cycle-adjusted), or ultrasound CRL/BPD measurements for trimester-specific accuracy.
📊 Multi-Method
Compare LMP, conception, ultrasound, IVF.
✓ Confidence
Each method gets a confidence score.
⚠️ Discrepancy
Flags when methods disagree >7 days.
How Does It Work?
IVF (95% confidence) > First-trimester US (90%) > Conception (85%) > LMP regular (75%). When first-trimester US and LMP differ >5-7 days, ACOG recommends using US date.
When to Use
New pregnancy, after ultrasound, IVF/ART, irregular cycles, dating uncertainty, or second opinion.
Naegele's Rule
EDD = LMP + 280 days. With cycle adjustment: EDD = LMP + 280 + (Cycle Length - 28). Assumes ovulation day 14 of 28-day cycle.
Conception Method
EDD = Conception Date + 266 days. Conception = 38 weeks before delivery. Reliable if ovulation was tracked.
Ultrasound Method
GA at US (days) = weeks × 7 + days. EDD = Ultrasound Date + (280 - GA at US). First trimester most accurate (±5-7 days).
IVF Transfer Method
Day 3: EDD = Transfer + 263. Day 5: +261. Day 6: +260. Most accurate—exact fertilization known.
Accuracy Notes
Only ~5% of babies born on exact due date. Most full-term births 39-41 weeks. Naegele accuracy ±14 days; first-trimester US ±5-7 days.
Frequently Asked Questions
Why do my LMP and ultrasound dates differ?
Common with irregular cycles, late ovulation, or cycle length variations. If the difference exceeds 7 days in the first trimester, your provider will typically use the ultrasound date as it's more accurate.
Which dating method is most accurate?
IVF transfer dating is most accurate (±1-2 days) since fertilization date is known. First-trimester ultrasound is next best (±5-7 days). LMP dating varies based on cycle regularity.
Can my due date change during pregnancy?
Your EDD should be established by your first prenatal visit and generally doesn't change. If first-trimester ultrasound shows significant discrepancy from LMP, the EDD may be adjusted.
What if I don't know my LMP?
Use other methods like conception date (if tracked) or ultrasound dating. This calculator allows any combination of available information without requiring LMP.
How accurate is the 280-day calculation?
The 280-day (40 weeks) calculation assumes ovulation on day 14 of a 28-day cycle. Only ~5% of babies are born on their exact due date. Most full-term births occur between 39-41 weeks.
What is Naegele's rule?
Naegele's rule: EDD = LMP + 280 days. Parikh's formula adjusts for cycle length: EDD = LMP + 280 + (cycle length - 28).