Pregnancy Due Date Calculator (2026)

We use Naegele's rule: your estimated due date (EDD) is the first day of your last menstrual period (LMP) plus 280 days (40 weeks), adjusted for your cycle length if it isn't 28 days. If you have a 32-day cycle, for example, the due date shifts about 4 days later, because ovulation happens later in a longer cycle.

It is an estimate. Only about 1 in 20 babies are born on their exact due date; most arrive within a window of roughly two weeks either side. A first-trimester dating ultrasound (measuring the baby) is more accurate than the LMP method, especially if your cycles are irregular or you are unsure of your LMP.

The LMP method needs the first day of your last period. If you don't know it, or your cycles are irregular, a dating scan at your first antenatal appointment is the reliable way to establish gestational age and due date. In Singapore, KKH, NUH, and private obstetricians routinely offer dating scans.

The first trimester runs from week 1 to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 to birth. This calculator shows which trimester you are currently in based on weeks since your LMP.