Our pregnancy due date calculator estimates your baby's arrival date based on the first day of your last menstrual period (LMP) or your known conception date. The standard pregnancy length is 40 weeks (280 days) from the first day of the last period, using Nägele's rule. The calculator also shows your current week of pregnancy, your estimated due date, and key milestones including the end of each trimester. Remember that only about 5% of babies are born on their exact due date — most arrive within two weeks either side. Always discuss your due date with your midwife or doctor, as they may adjust it based on your dating scan.