DueDateLab

Pregnancy Due Date Calculator

A free pregnancy due date calculator that estimates when a baby might arrive based on the date of the last menstrual period, a known conception date, or an IVF embryo transfer date. The LMP method applies Naegele's rule — adding 280 days (40 weeks) to the first day of the last period — which has been the standard clinical convention since the nineteenth century. The conception method adds 266 days to the date intercourse or insemination is believed to have occurred, and the IVF method counts forward from a day-5 blastocyst transfer (261 days) or a day-3 transfer (263 days). The calculator also shows gestational age in weeks and days from the LMP, the current trimester, and how many days remain to the estimated due date. Everything runs in your browser on the dates you enter — nothing is uploaded or stored. The result is a planning estimate, not medical advice, a clinical diagnosis, or a substitute for a dating ultrasound or prenatal care. Due dates are inherently uncertain: only about 4% of births occur on the exact predicted date, full-term delivery spans 37 to 42 weeks of gestation, and a first- or second-trimester ultrasound may adjust the estimate if the fetal measurements differ from the LMP calculation. Talk to your obstetrician, midwife, or other prenatal care provider about your individual situation.