Pregnancy Due Date Calculator

The Pregnancy Due Date Calculator estimates when a baby is due using Naegele's rule — adding 280 days (40 weeks) to the first day of the last menstrual period — the same method most doctors and midwives use for an initial estimate before an ultrasound refines it. Beyond the last-period method, this tool also supports calculating from a known conception date or an IVF embryo transfer date (3-day or 5-day), automatically converting each of those back to an equivalent "last period" starting point so the same 280-day rule applies consistently.

Along with the due date, the calculator shows your current gestational age in weeks and days, which trimester you're in, and the estimated conception date — useful context whether you're tracking early pregnancy milestones or explaining timelines to a healthcare provider. Gestational age is conventionally counted from the last menstrual period, not from conception, which is why a pregnancy is described as "40 weeks" even though conception happens around two weeks after the period starts.

IVF due dates are calculated slightly differently because the embryo's age at transfer is already known precisely, removing the guesswork of estimating ovulation timing — a 5-day (blastocyst) transfer is 5 days further along than a 3-day transfer on the same calendar date, so the equivalent last-period date shifts back by 19 days instead of 17 to keep the 280-day total accurate.

This is an estimation tool built on a well-known obstetric rule of thumb, not a diagnostic instrument — only about 5% of babies are born exactly on their calculated due date, and actual delivery can reasonably happen anywhere from about 38 to 42 weeks. Nothing you enter is sent anywhere; use this for general planning and always confirm dates and due-date estimates with your doctor or midwife, especially once an ultrasound provides a more precise measurement.