Last menstrual period
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Enter your last period date to calculate your due date
Calculate your estimated due date and full pregnancy timeline.
Enter your last period date to calculate your due date
The most common method is 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. If your cycle is longer or shorter, the calculator adjusts accordingly. Only about 5% of babies are born exactly on their due date — most arrive within two weeks either side.
Due date calculators give an estimated due date (EDD) based on your last period. Only about 5% of babies are born on their exact due date. An early ultrasound (before 14 weeks) is the most accurate way to confirm your due date.
A full-term pregnancy is 39–40 weeks. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42+ weeks. Babies born before 37 weeks are considered premature (preterm).
A pregnancy is typically 40 weeks (280 days) from the first day of your last menstrual period, or approximately 38 weeks from conception. This is divided into three trimesters of roughly 13 weeks each.
The first trimester covers weeks 1–13 of pregnancy. During this time, the baby's organs form, the heartbeat begins around week 6, and the risk of miscarriage is highest. Most women experience morning sickness during this period.
The baby's sex can usually be determined by ultrasound between weeks 18–20 during the anatomy scan. Some DNA blood tests (NIPT) can determine sex as early as 10 weeks into pregnancy.
If your cycle is shorter or longer than 28 days, your ovulation and conception date will differ. Our calculator adjusts for cycle length — a 35-day cycle shifts your estimated due date forward by 7 days compared to a 28-day cycle.