How is a due date calculated?
Most due dates use Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, we shift the date by the difference.
If you know your conception date, your due date is about 266 days (38 weeks) later. Pregnancy weeks are still counted from two weeks before conception.
Already dreaming about names? Try our baby name generator.