About this tool
Enter the first day of your last menstrual period and your average cycle length to estimate your due date with Naegele's rule (LMP plus 280 days) and see how many weeks pregnant you are. It runs locally in your browser.
Frequently asked questions
How is the due date calculated?
Naegele's rule adds 280 days (40 weeks) to the first day of your last period, then adjusts by the difference between your cycle length and 28 days.
Is this medically exact?
No — it is an estimate. Only about 4 percent of births happen on the due date, so treat it as a guide and confirm with your healthcare provider.