Due Date Calculator
Calculate your estimated due date based on your last menstrual period (LMP) using Naegele's rule.
Naegele's Rule.
How Your Pregnancy Due Date is Calculated
Predicting an estimated due date (EDD) is one of the first and most exciting steps of pregnancy. Knowing your due date helps you plan for the baby's arrival, schedule critical prenatal medical appointments, and track weekly developmental milestones. A standard human pregnancy lasts approximately 280 days (40 weeks) from the first day of the last menstrual period (LMP), although only about 4% of babies are born precisely on their calculated due date.
Naegele's Rule & Gestational Age Calculation
This calculator determines your due date using Naegele's Rule, a standardized clinical method. The calculation takes the first day of your last menstrual period, adds 7 days, subtracts 3 months, and adds 1 year. This formula assumes a standard 28-day menstrual cycle with ovulation occurring on day 14. If you have irregular cycles, the calculator can adjust the calculations based on your specific cycle length to provide a more accurate estimation of gestational age.
Tracking Trimesters & Prenatal Timelines
A full-term pregnancy is divided into three distinct trimesters, each marked by unique physiological changes and milestones. The first trimester (weeks 1–12) involves rapid organogenesis and fetal formation. The second trimester (weeks 13–26) is characterized by visible fetal growth and maternal stabilization. The third trimester (weeks 27–40) is the final growth phase where the baby prepares for birth. Monitoring these milestones helps ensure a healthy gestational progression for both mother and child.
Frequently Asked Questions
The standard method uses Naegele's Rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). This assumes a 28-day cycle with ovulation on day 14. The calculator also adjusts for custom cycle lengths if yours differs from the standard.
Only about 5% of babies are born on their exact due date. The estimate is accurate within a ±2-week window for most pregnancies. The most accurate dating comes from a first-trimester ultrasound (before 13 weeks), which measures the baby's crown-rump length and can be more precise than LMP calculations.
If your average cycle is longer or shorter than 28 days, the calculator adjusts the ovulation date accordingly. For example, a 35-day cycle shifts the estimated ovulation — and therefore the due date — forward by 7 days compared to the standard calculation.
A full-term pregnancy is between 39 and 40 weeks 6 days. Early term is 37–38 weeks 6 days, late term is 41–41 weeks 6 days, and post-term is 42+ weeks. Babies born before 37 weeks are premature and may need special medical care. Delivery after 42 weeks may also be medically managed.
For IVF pregnancies, the due date is typically calculated differently: embryo transfer date + 266 days for a day-3 transfer, or + 263 days for a day-5 blastocyst transfer. If you conceived via IVF, consult your fertility specialist who will provide a precise due date based on the embryo transfer date.