Pregnancy Due Date Calculator

How the due date is estimated

Doctors commonly estimate the due date (EDD, estimated date of delivery) using Naegele’s rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation around day 14. If your cycle is longer or shorter, the calculator shifts the date by the difference.

Counting pregnancy weeks

Pregnancy is counted from the first day of your last period, about two weeks before conception. So at “4 weeks pregnant”, the embryo is about 2 weeks old. This is the standard way doctors and scans count weeks.

Trimesters

• First trimester: weeks 1–13. Early development, often with nausea and tiredness.
• Second trimester: weeks 14–27. Many women feel better; the anomaly scan is usually around weeks 18–22.
• Third trimester: week 28 until birth. Growth, and preparing for delivery.

How accurate is it?

Only about 1 in 20 babies arrive on their due date; most arrive within two weeks either side. An early ultrasound, especially in the first trimester, often gives a more accurate date, and your doctor may adjust your EDD based on it. If you don’t remember your LMP or have irregular cycles, rely on your doctor’s dating scan.

Important

This calculator is for general information and is not medical advice. Please register your pregnancy with a doctor or health centre early for regular antenatal care, check-ups and supplements. For counting days to your due date, you can also use the countdown timer.

Example

If your last period started on 1 January 2026 and your cycle is 28 days, the estimated due date is 8 October 2026. On 12 March 2026 you would be 10 weeks pregnant, in the first trimester. With a 32-day cycle, the due date shifts four days later, to 12 October.

Consult your doctor.