Pregnancy Due Date Calculator

How is a due date calculated?

Your estimated due date (EDD) is most commonly calculated using Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This calculator uses that same method. It assumes a regular 28-day cycle with ovulation around day 14. Because pregnancy is dated from the LMP rather than conception, you are considered “two weeks pregnant” at the moment of conception — which is why the count can feel surprising at first.

How accurate is your due date?

A due date is an estimate, not a fixed appointment. Only around 1 in 20 babies are born on their exact due date. Most arrive within a window of roughly two weeks before or after. Babies born between 37 and 42 weeks are considered term. Your healthcare provider may adjust your due date after an early ultrasound, which measures the baby directly and is often more accurate than LMP dating, especially if your cycles are irregular or you are unsure of your LMP.

Understanding the trimesters

Pregnancy is divided into three trimesters. The first trimester (weeks 1 to 12) is when the baby's major organs form and is often accompanied by symptoms like nausea and fatigue. The second trimester (weeks 13 to 26) is frequently the most comfortable, with the anomaly scan typically performed around week 20. The third trimester (weeks 27 to 40) is when the baby grows rapidly and prepares for birth. This calculator shows which trimester you are in and your key upcoming milestones.

The importance of antenatal care

Regular antenatal (prenatal) care is one of the most important things you can do for a healthy pregnancy. The World Health Organization recommends a minimum of eight antenatal contacts during pregnancy to monitor your health and your baby's development, screen for complications such as pre-eclampsia and gestational diabetes, and provide guidance on nutrition and wellbeing. Booking your first appointment early — ideally before 12 weeks — gives you and your baby the best start.