Expected date of delivery is calculated by all EXCEPT

[Cl (266 days or 38 days) (64 - Dutta 6th)Duration 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 age**True gestation period is to be calculated by substracting 14 days from 280 days i.e. 266 day. This is called fertilization or ovulatory age