The time of pregnancy is calculated from the first day of your last menstrual period (LMP), which is typically two weeks before conception actually occurs. This means the first two weeks of the 40-week count are before fertilization, during which your body prepares for ovulation and a new cycle begins
Maybe it is not best explained, but the theory is accurate, another link: https://americanpregnancy.org/healthy-pregnancy/week-by-week/pregnancy-week-1-2/
Thanks, that one makes a bit more sense. And I mean the two things, the menstrual period and conception are linked… So there’s that 😆