Six focused guides on how a due date gets set, when a scan overrules it, and what the week counts actually mean. Each one names the source it draws from on the editorial standards page.
The arithmetic behind Naegele's rule, why it assumes a 28-day cycle, and when ACOG says an ultrasound should move the date instead.
Read →Why weeks are counted from your last period rather than conception, and how to find your current week without a due date handy.
Read →The three trimesters, their week ranges, and the milestones that mark each one, week by week.
Read →What a published study of confirmed ovulation dates says about how much a normal pregnancy actually varies.
Read →Two ways to estimate when you conceived, and why the honest answer is a window of days, not a single date.
Read →ACOG's early, full, late and post-term categories, and why the last two weeks before 40 matter more than the old "term" label suggested.
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