Due Date Calculator – Pregnancy EDD by LMP, Conception & IVF

A due date calculator estimates your Estimated Delivery Date (EDD) based on your Last Menstrual Period (LMP), conception date, or IVF transfer date. It uses Naegele's Rule, the globally accepted obstetric standard. The EDD is an estimate — about 80% of births occur within 2 weeks of the calculated date.

Using Naegele's Rule: EDD = First day of LMP + 280 days (40 weeks). This assumes a 28-day cycle. For longer or shorter cycles, the EDD is adjusted proportionally. For example, a 35-day cycle shifts the EDD 7 days later than calculated from standard 28-day LMP math.

Pregnancy duration is measured from the first day of the last menstrual period, which is about 2 weeks before conception. The actual fertilization-to-birth duration is approximately 38 weeks, but counting from LMP makes it 40 weeks. 'Nine months' is the colloquial approximation, but obstetric dating uses weeks for clinical precision.

LMP-based due dates are reasonably accurate but vary based on cycle regularity and timing of ovulation. Only about 5% of babies are born exactly on their EDD. Early ultrasound (8–12 weeks) measuring crown-rump length is the most accurate method for confirming gestational age. For irregular periods, ultrasound dating takes priority.

Yes. If you know your conception date, add 266 days (38 weeks). Our calculator handles this automatically. Note: identifying the exact conception date can be difficult unless you tracked ovulation or used assisted reproduction.

For IVF, add 263 days to a Day 3 embryo transfer date, or 261 days to a Day 5 blastocyst transfer date. Our calculator applies these adjustments automatically when you select the IVF method.

If cycles are irregular (shorter than 21 days or longer than 35 days), LMP-based dating is less reliable. A first-trimester ultrasound between 8 and 12 weeks provides more accurate gestational age measurement and is recommended for women with irregular cycles.

Full term is defined as 39–40 weeks 6 days of gestation. Early term is 37–38 weeks 6 days. Late term is 41–41 weeks 6 days. Post-term is 42 weeks or beyond. Babies born at full term generally have the best outcomes, though many healthy births occur between 37 and 42 weeks.

Most healthcare providers recommend the first prenatal visit at 8–10 weeks. However, contacting your OB/GYN, midwife, or general practitioner as soon as you confirm pregnancy is important to start appropriate prenatal care, folic acid supplementation, and screening tests.

Yes. Naegele's Rule is the international standard used by OB/GYN practitioners globally. This calculator supports all date formats and is used in India, USA, UK, Canada, Australia, UAE, and worldwide. The medical formulas are identical regardless of country.

Yes, the due date calculation is the same for twin or multiple pregnancies. However, twins often deliver earlier — typically 36–37 weeks for di-di twins and earlier for mono-mono or mono-di twins. Always follow your obstetrician's guidance for high-risk or multiple pregnancies.

Gestational age is counted from the first day of LMP. Fetal age (or embryonic age) is counted from fertilization, which typically occurs ~14 days after LMP. This is why gestational age is always approximately 2 weeks more than fetal age. Medical dating uses gestational age as the standard.