Calculate your baby's due date
The calculator primarily 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 Mittendorf-Williams method adjusts this slightly based on factors like maternal age and race.
Only about 5% of babies are born on their exact due date. A normal pregnancy can range from 37 to 42 weeks. The due date provides a reference point for tracking fetal development and scheduling prenatal care, not a precise prediction.
The calculator shows key trimester dates. The first trimester ends at week 12 (major organ formation complete). The second ends at week 27 (viability milestone). Full term is considered 39 weeks. These milestones help track your baby's development.
Attend all prenatal appointments. Take prenatal vitamins with folic acid. Maintain a balanced diet and stay hydrated. Get regular, moderate exercise as approved by your doctor. Avoid alcohol, smoking, and limit caffeine.
Due date calculators provide an estimated date, not an exact prediction. Only about 5% of babies are born on their exact due date. Most babies arrive within two weeks before or after the estimated due date. A full-term pregnancy can range from 37 to 42 weeks. First-time mothers tend to deliver slightly later, while subsequent pregnancies may deliver earlier. An early ultrasound (before 12 weeks) can improve accuracy by measuring the embryo directly.
The most common method is Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle with ovulation occurring on day 14. If your cycle is longer or shorter than 28 days, the calculator adjusts accordingly. Doctors may also use ultrasound measurements, especially in the first trimester, to estimate or confirm the due date based on the size of the embryo.
If you are unsure of your last menstrual period date, your doctor can estimate your due date using an early ultrasound scan. During the first trimester, ultrasound measurements of the embryo's crown-to-rump length are highly accurate for dating pregnancy, typically within 5-7 days. If you know your conception date, you can add 266 days (38 weeks) to estimate your due date. Your healthcare provider can help determine the most accurate estimate based on your individual situation.