Pregnancy Due Date Calculator
Estimate a pregnancy due date from the first day of the last menstrual period, with current progress and trimester.
Adjusts the estimate if your cycle isn't 28 days.
This estimates a due date from the first day of your last menstrual period (LMP) using Naegele's rule — about 280 days, adjusted for your cycle length. It's an estimate; only around 1 in 20 babies arrive on the exact date. Always follow your midwife or doctor's dating scan.
Frequently asked questions
The common method (Naegele's rule) adds 280 days — 40 weeks — to the first day of your last menstrual period, assuming a 28-day cycle. This calculator adjusts that if your cycle is longer or shorter.
It's an estimate. Only about 5% of babies are born on their exact due date; most arrive within a week or two either side. An early ultrasound (dating scan) gives a more precise estimate than the LMP method.