Calculate your estimated due date (EDD) using Naegele's rule from your last menstrual period, conception date, or IVF transfer date. View trimester timeline and key milestones.
The Due Date Calculator estimates your Expected Delivery Date (EDD) using Naegele's rule and multiple calculation methods. Knowing your due date helps you and your healthcare team plan prenatal care, schedule key ultrasounds, and prepare for delivery.
The most common method uses your last menstrual period (LMP): add 280 days (40 weeks) to the first day of your last period. If you know your conception date, the calculator adds 266 days. For IVF pregnancies, it uses the embryo transfer date plus 261 days (Day 3 transfer) or 259 days (Day 5 blastocyst transfer).
Only about 5% of babies are born on their exact due date, but 80% are born within two weeks of the EDD. Your healthcare provider may adjust the due date based on first-trimester ultrasound measurements. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
An accurate due date is the foundation of prenatal care. It determines when to schedule genetic screening tests, anatomy scans, glucose tolerance tests, and group B strep screening. It's also essential for identifying preterm labor (<37 weeks), post-term pregnancy (>42 weeks), and calculating fetal age for growth assessment. Having a precise figure at your fingertips empowers better planning and more confident decisions.
Method 1 — Last Menstrual Period (Naegele's Rule): EDD = LMP + 280 days Method 2 — Conception Date: EDD = Conception + 266 days Method 3 — IVF Transfer: EDD (Day 3) = Transfer + 263 days EDD (Day 5) = Transfer + 261 days Gestational Age (weeks) = (Today − LMP) / 7 Trimester 1: Weeks 0–13 Trimester 2: Weeks 14–27 Trimester 3: Weeks 28–40+
Result: Due Date: October 8, 2026
EDD = January 1 + 280 days = October 8, 2026. If today were March 15, 2026, the gestational age would be 10 weeks 3 days, placing the pregnancy in the first trimester with the anatomy scan coming at approximately 18–20 weeks.
Franz Karl Naegele, a German obstetrician, published his rule in 1812: add one year, subtract three months, and add seven days to the LMP. This is equivalent to adding 280 days and has been the standard dating method for over two centuries despite its well-known limitations.
The first trimester (weeks 1–13) is the period of organogenesis when major structures form. The second trimester (weeks 14–27) involves rapid growth and organ maturation — this is when most women feel best. The third trimester (weeks 28–40) focuses on fetal weight gain and lung maturity, with the fetus doubling in weight during the final 8 weeks.
Research has shown that the average pregnancy lasts 268 days from ovulation — slightly shorter than Naegele's 280 days from LMP. First-time mothers tend to deliver slightly later than multiparous women. Machine learning models incorporating ultrasound biometry, maternal characteristics, and biomarkers are being studied to provide more personalized due date predictions.
Naegele's rule assumes a 28-day cycle and ovulation on day 14. It is reasonably accurate for women with regular 28-day cycles but can be off by one to two weeks for those with irregular or longer cycles. First-trimester ultrasound is considered the gold standard for pregnancy dating.
ACOG guidelines recommend adjusting the due date when the ultrasound-based estimate differs by more than 5 days (before 9 weeks), 7 days (9–15 weeks), or 10 days (16–21 weeks). In these cases, the ultrasound date takes precedence.
Gestational age counts from the first day of the LMP and is the standard clinical measurement (40 weeks total). Fetal age (embryonic age) counts from conception and is about 2 weeks shorter (38 weeks). Healthcare providers use gestational age for all clinical decisions.
The due date may be adjusted once based on a first-trimester ultrasound. After that, it should not be changed because later ultrasound measurements have increasing variability. ACOG recommends establishing a final EDD by the first prenatal visit.
Pregnancies beyond 41 weeks are considered late-term, and beyond 42 weeks are post-term. Post-term pregnancies carry increased risks including oligohydramnios, macrosomia, and stillbirth. Most providers discuss induction between 39 and 41 weeks based on individual risk factors.
Not precisely. A positive home test usually occurs around 4 weeks gestational age (2 weeks after conception), but the exact detection day varies. For the most accurate dating, you need either your LMP date, conception date, or a dating ultrasound.