<prompt> Expected date of delivery is calculated by all EXCEPTNine calender months plus 7 days280 days or 40 weeks266 days or 38 weaks10 lunar months  <response>: Cl 266 days or 38 days 64 - Dutta 6thDuration of Pregnancy - Calculated by clinicians in terms of 10 lunnar months or 9 calender months and 7days or 280 days or 40 weeks, calculated from the first day of the last menstrual period. This is called menstrual ageTrue gestation period is to be calculated by substracting 14 days from 280 days i.e. 266 day. This is called fertilization or ovulatory age 