The Due Date Calculator estimates the delivery date of a pregnant woman based on her last menstrual period (LMP), ultrasound, conception date, or IVF transfer date.
Pregnancy is typically measured in gestational age, starting from the first day of the woman's last menstrual period (LMP). A full-term pregnancy is considered to be 40 weeks (280 days)from the LMP, which is approximately 38 weeks from conception.
The most common method for estimating a due date is using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This is adjusted when the average cycle length differs from the standard 28-day cycle — add or subtract one day for each day the cycle differs from 28 days.
An ultrasound performed in early pregnancy (ideally before 14 weeks) can measure the size of the embryo or fetus to estimate gestational age. The ultrasound date and the reported gestational age in weeks and days are used to back-calculate the LMP equivalent, from which the due date is derived.
If the conception date is known (e.g., from fertility tracking), the due date is estimated as conception date + 266 days (38 weeks). Conception typically occurs approximately 14 days after the LMP for a 28-day cycle.
For pregnancies achieved through in vitro fertilization (IVF), the due date is calculated from the embryo transfer date. A Day-3 embryo transfer adds 263 days (266 − 3); a Day-5 blastocyst transfer adds 261 days (266 − 5) to the transfer date.
Note: Only about 4% of births occur on the estimated due date. The calculator provides an estimate — your healthcare provider may adjust dates based on clinical assessments.
Find your estimated due date quickly with our free calculator, using your last menstrual period date or known conception date.
Standard estimation adds 280 days to the first day of your last menstrual period (Naegele's Rule), or 266 days if calculating from a known conception date.
This tool focuses specifically on due date estimation; the Pregnancy Calculator also tracks current week and trimester progress.
It's a standard medical estimate, actual delivery dates vary naturally by up to two weeks in either direction.
Yes, early ultrasound measurements are often considered more accurate and may adjust your official due date.
Multiple pregnancies often result in earlier delivery on average; consult your healthcare provider for guidance.