Pregnancy due date calculator
Estimate your due date and current week of pregnancy from the date of your last menstrual period or an estimated conception date, using Naegele's rule, which is commonly used in obstetrics. Calculated locally, with no data transmitted.
How it works
Naegele's rule, used since the 19th century and still a reference in obstetrics, estimates the delivery date by adding 280 days (40 weeks) to the first day of the last menstrual period, assuming a regular 28-day cycle with ovulation on day 14. If you know your exact conception date (for example from fertility tracking), the tool adds 266 days to that date instead.
Why is pregnancy counted in weeks from the last menstrual period?
By medical convention, gestational age is counted from the first day of the last menstrual period rather than from actual conception (which happens about two weeks later). That is why a pregnancy "lasts" 40 weeks of amenorrhea, even though the development of the embryo and then the fetus actually covers only about 38 weeks.
Why does the actual delivery date often differ from the estimated date?
Only about 5% of babies are born exactly on the calculated date: the actual length of gestation naturally varies by several days depending on the woman, cycle regularity and other individual factors. A first-trimester ultrasound performed by a healthcare professional remains the most reliable way to date a pregnancy precisely.
This health information stays strictly on your device: nothing is sent to a server or kept after you close the page.