Pregnancy Due Date Calculator — estimate your baby's arrival from your last menstrual period (LMP), conception date, IVF transfer date, or ultrasound gestational age. Uses Naegele's Rule (LMP + 280 days, adjusted for cycle length) and includes a full trimester timeline, key milestones, and countdown to your due date.
Pregnancy Due Date Calculator
Calculate your estimated due date (EDD) using LMP, conception date, IVF transfer date, or ultrasound. Includes milestones and trimester breakdown.
How Due Dates Are Calculated
The standard method is Naegele's Rule, developed by German obstetrician Franz Karl Naegele in 1812. It estimates the due date as 280 days (40 weeks) from the first day of the last menstrual period. This assumes ovulation at day 14 of a 28-day cycle. For longer or shorter cycles, the calculator adjusts the ovulation estimate accordingly.
| Method | Formula |
|---|---|
| LMP Method | LMP + 280 days (+ cycle adjustment) |
| Conception Date | Conception date + 266 days (38 weeks) |
| IVF Day 5 Transfer | Transfer date + 261 days |
| IVF Day 3 Transfer | Transfer date + 263 days |
| Ultrasound | Scan date − gestational age at scan + 280 days |
Worked example: LMP = April 1, 2026. Standard 28-day cycle. EDD = April 1 + 280 days = January 5, 2027. If cycle is 35 days (ovulation at day 21 instead of 14), add 7 days: EDD = January 12, 2027. At a July 1 anatomy scan, the pregnancy would be at 13 weeks 0 days, well into the second trimester.
👶 OB-GYN Insight
Why Your Due Date Will Likely Change After Your First Ultrasound: LMP-based dating is just an estimate — it assumes regular cycles and average ovulation timing. A first-trimester ultrasound (weeks 8–12) uses the crown-rump length (CRL) measurement, which has a margin of error of only ±5–7 days, compared to ±2 weeks for LMP dating. If the ultrasound date differs by more than 5–7 days from the LMP date, OBs typically adjust the EDD to match the ultrasound. Early ultrasound is the gold standard for accurate dating. Third-trimester ultrasounds have a margin of error of ±3 weeks and are not used for dating.
Pregnancy Due Date Calculator
Most cycles are 21–35 days; 28 is average
Pregnancy Due Date FAQ
How accurate is the estimated due date?
Only ~4% of babies arrive exactly on their due date. About 80% are born within 2 weeks before or after. Early ultrasounds (before 12 weeks) are the most accurate dating method, with a margin of error of ±5–7 days. Third-trimester ultrasounds can be off by ±3 weeks due to normal size variation.
What is gestational age vs. fetal age?
Gestational age counts from LMP, so at conception you are already "2 weeks pregnant." Fetal age counts from conception and is always ~2 weeks less. All clinical measurements use gestational age — this is what your doctor and this calculator use.
When does each trimester begin?
First trimester: weeks 1–12. Second trimester: weeks 13–27. Third trimester: week 28 until birth. "Full term" is 37–40 weeks. Babies born at 37 weeks are early term; 39–40 weeks is considered full term; 41+ weeks is late term.
How is an IVF due date calculated differently?
For a day 5 blastocyst IVF transfer: due date = transfer date + 261 days. For a day 3 embryo: transfer date + 263 days. These are precise because fertilization date is known exactly. Your clinic will confirm via early ultrasound.
What is the viability milestone at week 24?
At 24 weeks, a premature baby has approximately a 50–60% survival rate with intensive NICU care. This rises to 90%+ by 28 weeks and 99%+ by 32 weeks. Week 24 is an important medical and legal threshold but does not change routine prenatal care for ongoing pregnancies.