The standard duration used to calculate a due date – roughly 40 weeks from the last menstrual period – is a statistical average, not a fixed rule. There are medically documented cases of pregnancies that significantly exceeded this average, which is why the word “probable” is, in fact, more accurate than “exact.”
The variation is completely normal: individual factors – from menstrual cycle length to physiological particularities – can shift the actual birth date by one or two weeks from the initial estimate, without indicating any problem at all.
That’s why any due-date calculation should be treated as a useful planning reference, not an exact prophecy – medical practice itself treats the “due date” as a window, not a fixed day on the calendar.
A simple detail that slightly shifts expectations around an otherwise very popular calculation.
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